diff --git a/language/types.xml b/language/types.xml index 5db9a34bd5..2976caacfe 100644 --- a/language/types.xml +++ b/language/types.xml @@ -1,9 +1,9 @@ - - - Types + + + Types - + Introduction @@ -104,6 +104,7 @@ And the pseudo-variable $.... + You may also find some references to the type "double". Consider double the same as float, the two names exist only for historic @@ -115,12 +116,14 @@ rather, it is decided at runtime by PHP depending on the context in which that variable is used. + If you want to check out the type and value of a certain expression, use var_dump. + If you simply want a human-readable representation of the type for debugging, use gettype. To check for a certain type, @@ -155,12 +158,14 @@ if (is_string($a_bool)) { + If you would like to force a variable to be converted to a certain type, you may either cast the variable or use the settype function on it. + Note that a variable may be evaluated with different values in certain situations, depending on what type it is at the time. For more @@ -183,7 +188,7 @@ if (is_string($a_bool)) { &language.types.psuedo-types; &language.types.type-juggling; - + - - Arrays + + + Arrays - - An array in PHP is actually an ordered map. A map is a type that - maps values to keys. - This type is optimized in several ways, - so you can use it as a real array, or a list (vector), - hashtable (which is an implementation of a map), - dictionary, collection, - stack, queue and probably more. Because you can have another - PHP array as a value, you can also quite easily simulate - trees. - - - Explanation of those data structures is beyond the scope of this - manual, but you'll find at least one example for each of them. - For more information we refer you to external literature about - this broad topic. - + + An array in PHP is actually an ordered map. A map is a type that maps + values to keys. This type is + optimized in several ways, so you can use it as a real array, or a list + (vector), hashtable (which is an implementation of a map), dictionary, + collection, stack, queue and probably more. Because you can have another PHP + array as a value, you can also quite easily simulate trees. + + + Explanation of those data structures is beyond the scope of this manual, but + you'll find at least one example for each of them. For more information we + refer you to external literature about this broad topic. + - - Syntax - - - Specifying with <function>array</function> - - An array can be created by the array - language-construct. It takes a certain number of comma-separated - key => value - pairs. - - - + + Syntax + + + Specifying with <function>array</function> + + An array can be created by the array + language-construct. It takes a certain number of comma-separated + key => + value pairs. + + + array( key => value - , ... - ) + , ... + ) // key may be an integer or string // value may be any value - - - - - + + + + + "bar", 12 => true); @@ -53,26 +48,23 @@ echo $arr["foo"]; // bar echo $arr[12]; // 1 ?> ]]> - - - - - A key may be either an - integer or a string. If a key is - the standard representation of an integer, it will - be interpreted as such (i.e. "8" will be - interpreted as 8, while - "08" will be interpreted as - "08"). - Floats in key are truncated to integer. - There are no different indexed and - associative array types in PHP; there is only one array type, - which can both contain integer and string indices. - - - A value can be of any PHP type. - - + + + + + A key may be either an integer or a + string. If a key is the standard representation of an + integer, it will be interpreted as such (i.e. + "8" will be interpreted as 8, while + "08" will be interpreted as "08"). + Floats in key are truncated to integer. + There are no different indexed and associative array types in PHP; there is + only one array type, which can both contain integer and string indices. + + + A value can be of any PHP type. + + array(6 => 5, 13 => 9, "a" => 42)); @@ -82,16 +74,16 @@ echo $arr["somearray"][13]; // 9 echo $arr["somearray"]["a"]; // 42 ?> ]]> - - - - - If you do not specify a key for a given value, then the maximum - of the integer indices is taken, and the new key will be that - maximum value + 1. If you specify a key that already has a value - assigned to it, that value will be overwritten. - - + + + + + If you do not specify a key for a given value, then the maximum of the + integer indices is taken, and the new key will be that maximum value + 1. If + you specify a key that already has a value assigned to it, that value will + be overwritten. + + 43, 32, 56, "b" => 12); array(5 => 43, 6 => 32, 7 => 56, "b" => 12); ?> ]]> - - - - - - As of PHP 4.3.0, the index generation behaviour described - above has changed. Now, if you append to an array in which - the current maximum key is negative, then the next key - created will be zero (0). Before, the new - index would have been set to the largest existing key + 1, - the same as positive indices are. - - - - Using &true; as a key will evaluate to integer - 1 as key. Using &false; as a key will evaluate - to integer 0 as key. Using - NULL as a key will evaluate to the empty - string. Using the empty string as key will create (or overwrite) - a key with the empty string and its value; it is not the same as - using empty brackets. - - - You cannot use arrays or objects as keys. Doing so will result in a - warning: Illegal offset type. - - - - - Creating/modifying with square-bracket syntax - - You can also modify an existing array by explicitly setting - values in it. - - - This is done by assigning values to the array while specifying the - key in brackets. You can also omit the key, add an empty pair - of brackets ("[]") to the variable name in that case. - + + + + + + As of PHP 4.3.0, the index generation behaviour described above has + changed. Now, if you append to an array in which the current maximum key is + negative, then the next key created will be zero (0). + Before, the new index would have been set to the largest existing key + 1, + the same as positive indices are. + + + + Using &true; as a key will evaluate to integer + 1 as key. Using &false; as a key will evaluate to + integer 0 as key. Using + NULL as a key will evaluate to the empty string. Using + the empty string as key will create (or overwrite) a key with the empty + string and its value; it is not the same as using empty brackets. + + + You cannot use arrays or objects as keys. Doing so will result in a warning: + Illegal offset type. + + + + + Creating/modifying with square-bracket syntax + + You can also modify an existing array by explicitly setting values in it. + + + This is done by assigning values to the array while specifying the key in + brackets. You can also omit the key, add an empty pair of brackets + ("[]") to the variable name in that case. + $arr[key] = value; $arr[] = value; // key may be an integer or string // value may be any value - - If $arr doesn't exist yet, it will be created. - So this is also an alternative way to specify an array. - To change a certain value, just assign a new value - to an element specified with its key. If you want to - remove a key/value pair, you need to unset it. - - + + If $arr doesn't exist yet, it will be created. So this is + also an alternative way to specify an array. To change a certain value, just + assign a new value to an element specified with its key. If you want to + remove a key/value pair, you need to unset it. + + 1, 12 => 2); @@ -167,39 +155,37 @@ unset($arr[5]); // This removes the element from the array unset($arr); // This deletes the whole array ?> ]]> - - - - - - As mentioned above, if you provide the brackets with no key - specified, then the maximum of the existing integer indices is - taken, and the new key will be that maximum value + 1 . If no - integer indices exist yet, the key will be 0 - (zero). If you specify a key that already has a value assigned - to it, that value will be overwritten. - - - - - As of PHP 4.3.0, the index generation behaviour described - above has changed. Now, if you append to an array in which - the current maximum key is negative, then the next key - created will be zero (0). Before, the new - index would have been set to the largest existing key + 1, - the same as positive indices are. - - - - - Note that the maximum integer key used for this need - not currently exist in the array. It simply must - have existed in the array at some time since the last time the - array was re-indexed. The following example illustrates: - + + + + + + As mentioned above, if you provide the brackets with no key specified, then + the maximum of the existing integer indices is taken, and the new key will + be that maximum value + 1 . If no integer indices exist yet, the key will + be 0 (zero). If you specify a key that already has a + value assigned to it, that value will be overwritten. + + + + + As of PHP 4.3.0, the index generation behaviour described above has + changed. Now, if you append to an array in which the current maximum key + is negative, then the next key created will be zero + (0). Before, the new index would have been set to the + largest existing key + 1, the same as positive indices are. + + + + + Note that the maximum integer key used for this need not + currently exist in the array. It simply must have existed in the + array at some time since the last time the array was re-indexed. The + following example illustrates: + - - + + ]]> - - &example.outputs; - + + &example.outputs; + 7 ) ]]> - - + + - - - - - - Useful functions - - There are quite a few useful functions for working with arrays. - See the array functions section. - - - - The unset function allows unsetting keys of an - array. Be aware that the array will NOT be reindexed. If you only - use "usual integer indices" (starting from zero, increasing by one), - you can achieve the reindex effect by using array_values. - - + + + + + + Useful functions + + There are quite a few useful functions for working with arrays. See the + array functions section. + + + + The unset function allows unsetting keys of an array. + Be aware that the array will NOT be reindexed. If you only use "usual + integer indices" (starting from zero, increasing by one), you can achieve + the reindex effect by using array_values. + + 'one', 2 => 'two', 3 => 'three'); @@ -283,30 +269,29 @@ $b = array_values($a); // Now $b is array(0 => 'one', 1 =>'three') ?> ]]> - - - - - - - The foreach - control structure exists specifically for arrays. It - provides an easy way to traverse an array. - - + + - - Array do's and don'ts + + + + The foreach control + structure exists specifically for arrays. It provides an easy way to traverse + an array. + + + + + Array do's and don'ts - - Why is <literal>$foo[bar]</literal> wrong? - - You should always use quotes around a string literal - array index. For example, use $foo['bar'] and not - $foo[bar]. But why is $foo[bar] wrong? You might have seen the - following syntax in old scripts: - - + + Why is <literal>$foo[bar]</literal> wrong? + + You should always use quotes around a string literal array index. For + example, use $foo['bar'] and not $foo[bar]. But why is $foo[bar] wrong? You + might have seen the following syntax in old scripts: + + ]]> - - - This is wrong, but it works. Then, why is it wrong? The reason - is that this code has an undefined constant (bar) rather than a - string ('bar' - notice the quotes), and PHP may in future define - constants which, unfortunately for your code, have the same - name. It works because PHP automatically converts a - bare string (an unquoted string which does - not correspond to any known symbol) into a string which contains - the bare string. For instance, if there is no defined constant - named bar, then PHP will substitute in the - string 'bar' and use that. - - - - This does not mean to always quote the - key. You do not want to quote keys which are constants or variables, as this will - prevent PHP from interpreting them. - - - + + + This is wrong, but it works. Then, why is it wrong? The reason is that this + code has an undefined constant (bar) rather than a string ('bar' - notice + the quotes), and PHP may in future define constants which, unfortunately for + your code, have the same name. It works because PHP automatically converts + a bare string (an unquoted string which does not + correspond to any known symbol) into a string which contains the bare + string. For instance, if there is no defined constant named + bar, then PHP will substitute in the string + 'bar' and use that. + + + + This does not mean to always quote the key. You do not + want to quote keys which are + constants or + variables, as this will prevent + PHP from interpreting them. + + + ]]> - - - &example.outputs; - + + + &example.outputs; + - - - - More examples to demonstrate this fact: - - + + + + More examples to demonstrate this fact: + + ]]> - - - - - When you turn error_reporting up to show - E_NOTICE level errors (such as setting - it to E_ALL) then you will see these - errors. By default, - error_reporting is turned down to not show them. - - - As stated in the syntax section, - there must be an expression between the square brackets - ('[' and ']'). That means - that you can write things like this: - - + + + + + When you turn error_reporting up to show + E_NOTICE level errors (such as setting it to + E_ALL) then you will see these errors. By default, + error_reporting is turned down to + not show them. + + + As stated in the syntax + section, there must be an expression between the square brackets + ('[' and ']'). That means that you + can write things like this: + + ]]> - - - This is an example of using a function return value - as the array index. PHP also knows about constants, - as you may have seen the E_* ones - before. + + + This is an example of using a function return value as the array index. PHP + also knows about constants, as you may have seen the E_* + ones before. - - + + ]]> - - - Note that E_ERROR is also a valid identifier, - just like bar in the first example. But the last - example is in fact the same as writing: - - + + + Note that E_ERROR is also a valid identifier, just like + bar in the first example. But the last example is in fact + the same as writing: + + ]]> - - - because E_ERROR equals 1, etc. - - - As we already explained in the above examples, - $foo[bar] still works but is wrong. - It works, because bar is due to its syntax - expected to be a constant expression. However, in this case no - constant with the name bar exists. PHP now - assumes that you meant bar literally, - as the string "bar", but that you forgot - to write the quotes. - - - So why is it bad then? - - At some point in the future, the PHP team might want to add another - constant or keyword, or you may introduce another constant into your - application, and then you get in trouble. For example, - you already cannot use the words empty and - default this way, since they are special - reserved keywords. - - - - To reiterate, inside a double-quoted string, it's - valid to not surround array indexes with quotes so - "$foo[bar]" is valid. See the above - examples for details on why as well as the section on - variable parsing - in strings. - - - - - - - - Converting to array - + + + because E_ERROR equals 1, etc. + + + As we already explained in the above examples, $foo[bar] + still works but is wrong. It works, because bar is due to + its syntax expected to be a constant expression. However, in this case no + constant with the name bar exists. PHP now assumes that + you meant bar literally, as the string + "bar", but that you forgot to write the quotes. + + + So why is it bad then? - For any of the types: integer, float, - string, boolean and resource, - if you convert a value to an array, you get an array - with one element (with index 0), which is the scalar value you - started with. + At some point in the future, the PHP team might want to add another + constant or keyword, or you may introduce another constant into your + application, and then you get in trouble. For example, you already cannot + use the words empty and default this + way, since they are special + reserved keywords. - - - If you convert an object to an array, you get the - properties (member variables) of that object as the array's elements. - The keys are the member variable names with a few notable exceptions: - private variables have the class name prepended to the variable name; - protected variables have a '*' prepended to the variable name. - These prepended values have null bytes on either side. This can result - in some unexpected behaviour. - - + + + To reiterate, inside a double-quoted string, it's valid to + not surround array indexes with quotes so "$foo[bar]" + is valid. See the above examples for details on why as well as the section + on variable parsing in + strings. + + + + + + + + Converting to array + + + For any of the types: integer, float, + string, boolean and resource, if you + convert a value to an array, you get an array with one element + (with index 0), which is the scalar value you started with. + + + + If you convert an object to an array, you get the properties + (member variables) of that object as the array's elements. The keys are the + member variable names with a few notable exceptions: private variables have + the class name prepended to the variable name; protected variables have a '*' + prepended to the variable name. These prepended values have null bytes on + either side. This can result in some unexpected behaviour. + + ]]> - - + + - The above will appear to have two keys named 'AA', although one - of them is actually named '\0A\0A'. - - - - If you convert a &null; value to an array, you get an empty array. - - + The above will appear to have two keys named 'AA', although one of them is + actually named '\0A\0A'. + + + + If you convert a &null; value to an array, you get an empty array. + + - - Comparing - - It is possible to compare arrays by array_diff and - by Array operators. - - + + Comparing + + It is possible to compare arrays by array_diff and by + Array operators. + + - - Examples - - The array type in PHP is very versatile, so here will be some - examples to show you the full power of arrays. - - - - + + Examples + + The array type in PHP is very versatile, so here will be some examples to + show you the full power of arrays. + + + + ]]> - - - - - - Using array() - + + + + + + Using array() + - - + + - - Collection - + + Collection + ]]> - - &example.outputs; - + + &example.outputs; + - - - - - Changing values of the array directly is possible since PHP 5 by passing - them as reference. Prior versions need workaround: - - Collection - + + + + + Changing values of the array directly is possible since PHP 5 by passing them + as reference. Prior versions need workaround: + + Collection + $color) { print_r($colors); ?> ]]> - - &example.outputs; - + + &example.outputs; + YELLOW ) ]]> - - - - - This example creates a one-based array. - - One-based index - + + + + + This example creates a one-based array. + + One-based index + 'January', 'February', 'March'); print_r($firstquarter); ?> ]]> - - &example.outputs; - + + &example.outputs; + 'March' ) ]]> - - - - - Filling an array - + + + + + Filling an array + ]]> - - - - Arrays are ordered. You can also change the order using various - sorting functions. See the array - functions section for more information. You can count - the number of items in an array using the - count function. - - - Sorting an array - + + + + Arrays are ordered. You can also change the order using various sorting + functions. See the array functions section + for more information. You can count the number of items in an array using the + count function. + + + Sorting an array + ]]> - - - - Because the value of an array can be anything, it can also be - another array. This way you can make recursive and - multi-dimensional arrays. - - - Recursive and multi-dimensional arrays - + + + + Because the value of an array can be anything, it can also be another array. + This way you can make recursive and multi-dimensional arrays. + + + Recursive and multi-dimensional arrays + array ( "a" => "orange", @@ -809,16 +784,15 @@ unset($fruits["holes"][0]); // remove "first" $juices["apple"]["green"] = "good"; ?> ]]> - - - - You should be aware that array assignment always involves - value copying. It also means that the internal array pointer used by - current and similar functions is reset. - You need to use the reference operator to copy - an array by reference. - - + + + + You should be aware that array assignment always involves value copying. It + also means that the internal array pointer used by + current and similar functions is reset. You need to use + the reference operator to copy an array by reference. + + ]]> - - - - - + + + + + - - Booleans - - - This is the easiest type. A boolean expresses a - truth value. It can be either &true; or &false;. - + + + Booleans + + + This is the easiest type. A boolean expresses a truth value. It + can be either &true; or &false;. + - - - The boolean type was introduced in PHP 4. - - + + + The boolean type was introduced in PHP 4. + + - - Syntax - - To specify a boolean literal, use either the keyword &true; - or &false;. Both are case-insensitive. - - + + Syntax + + To specify a boolean literal, use either the keyword &true; or &false;. Both + are case-insensitive. + + ]]> - - - - - Usually you - use some kind of operator - which returns a boolean value, and then pass it - on to a control - structure. - - + + + + + Usually you use some kind of + operator which returns a + boolean value, and then pass it on to a + control structure. + + ]]> - - - - + + + + - - Converting to boolean + + Converting to boolean + + To explicitly convert a value to boolean, use either the + (bool) or the (boolean) cast. However, + in most cases you do not need to use the cast, since a value will be + automatically converted if an operator, function or control structure + requires a boolean argument. + + + See also Type Juggling. + + + + When converting to boolean, the following values are considered + &false;: + + + - To explicitly convert a value to boolean, use either - the (bool) or the (boolean) cast. - However, in most cases you do not need to use the cast, since a value - will be automatically converted if an operator, function or - control structure requires a boolean argument. + the boolean &false; itself + + - See also Type Juggling. + the integer 0 (zero) - - - When converting to boolean, the following values - are considered &false;: - - - - the boolean - &false; itself - - - the integer 0 (zero) - - - the float - 0.0 (zero) - - - the empty string, and the string - "0" - - - an array - with zero elements - - - an object - with zero member variables (PHP 4 only) - - - the special type NULL (including unset variables) - - - - SimpleXML - objects created from empty tags - - - - - Every other value is considered &true; (including any - resource). - - - -1 is considered - &true;, like any other non-zero (whether negative - or positive) number! - - - - + + + + the float 0.0 (zero) + + + + + the empty string, and the + string "0" + + + + + an array with zero elements + + + + + an object with zero member + variables (PHP 4 only) + + + + + the special type NULL + (including unset variables) + + + + + SimpleXML objects created from empty + tags + + + + + Every other value is considered &true; (including any + resource). + + + -1 is considered &true;, like any other non-zero + (whether negative or positive) number! + + + + ]]> - - - - - - + + + + + + - - Floating point numbers - - Floating point numbers (AKA "floats", "doubles" or "real numbers") can be - specified using any of the following syntaxes: - - + + + Floating point numbers + + + Floating point numbers (AKA "floats", "doubles" or "real numbers") can be + specified using any of the following syntaxes: + + + ]]> - - - Formally: - - + + + + Formally: + + + - - - The size of a float is platform-dependent, - although a maximum of ~1.8e308 with a precision of roughly 14 - decimal digits is a common value (that's 64 bit IEEE format). - - - - Floating point precision - - It is quite usual that simple decimal fractions like - 0.1 or 0.7 cannot be - converted into their internal binary counterparts without a - little loss of precision. This can lead to confusing results: for - example, floor((0.1+0.7)*10) will usually - return 7 instead of the expected - 8 as the result of the internal representation - really being something like 7.9999999999.... - - - This is related to the fact that it is impossible to exactly - express some fractions in decimal notation with a finite number - of digits. For instance, 1/3 in decimal form - becomes 0.3333333. . .. - - - So never trust floating number results to the last digit and - never compare floating point numbers for equality. If you really - need higher precision, you should use the arbitrary precision math functions - or gmp functions instead. - - + + - - Converting to float - - - For information on when and how strings are converted to floats, - see the section titled String - conversion to numbers. For values of other types, the conversion - is the same as if the value would have been converted to integer - and then to float. See the Converting - to integer section for more information. - As of PHP 5, notice is thrown if you try to convert object to float. - - - + The size of a float is platform-dependent, + although a maximum of ~1.8e308 with a precision of roughly 14 + decimal digits is a common value (that's 64 bit IEEE format). + + + + Floating point precision + + + It is quite usual that simple decimal fractions like 0.1 + or 0.7 cannot be converted into their internal binary + counterparts without a little loss of precision. This can lead to confusing + results: for example, floor((0.1+0.7)*10) will usually + return 7 instead of the expected 8 as + the result of the internal representation really being something like + 7.9999999999.... + + + + This is related to the fact that it is impossible to exactly express some + fractions in decimal notation with a finite number of digits. For instance, + 1/3 in decimal form becomes + 0.3333333. . .. + + + So never trust floating number results to the last digit and never compare + floating point numbers for equality. If you really need higher precision, you + should use the arbitrary precision math + functions or gmp functions instead. + + + + + Converting to float + + + For information on when and how strings are converted to floats, see the + section titled String + conversion to numbers. For values of other types, the conversion is + the same as if the value would have been converted to integer and then to + float. See the Converting to + integer section for more information. As of PHP 5, notice is thrown if + you try to convert object to float. + + + + - - Integers - - - An integer is a number of the set - Z = {..., -2, -1, 0, 1, 2, ...}. - - - - See also: - Arbitrary length integer / GMP, - Floating point numbers, and - Arbitrary precision / BCMath - + + + Integers + + + An integer is a number of the set + Z = {..., -2, -1, 0, 1, 2, ...}. + + + + See also: + Arbitrary length integer / GMP, + Floating point numbers, and + Arbitrary precision / BCMath + - - Syntax - - Integers can be specified in decimal (10-based), hexadecimal (16-based) - or octal (8-based) notation, optionally preceded by a sign (- or +). - - - If you use the octal notation, you must precede the number with a - 0 (zero), to use hexadecimal notation precede - the number with 0x. - - Integer literals - + + Syntax + + + Integers can be specified in decimal (10-based), hexadecimal (16-based) or + octal (8-based) notation, optionally preceded by a sign (- or +). + + + + If you use the octal notation, you must precede the number with a + 0 (zero), to use hexadecimal notation precede the number + with 0x. + + + Integer literals + ]]> - - - Formally the possible structure for integer literals is: - - + + + + Formally the possible structure for integer literals is: + + + - - - The size of an integer is platform-dependent, although a - maximum value of about two billion is the usual value - (that's 32 bits signed). PHP does not support unsigned - integers. - Integer size can be determined from PHP_INT_SIZE, - maximum value from PHP_INT_MAX since PHP 4.4.0 and - PHP 5.0.5. - - - - If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest - of the number is ignored. - - Octal weirdness - + + + + The size of an integer is platform-dependent, although a maximum value of + about two billion is the usual value (that's 32 bits signed). PHP does not + support unsigned integers. Integer size can be determined from + PHP_INT_SIZE, maximum value from + PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5. + + + + + If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest of + the number is ignored. + + + Octal weirdness + ]]> - - - - - - - - Integer overflow - - If you specify a number beyond the bounds of the integer - type, it will be interpreted as a float instead. Also, if - you perform an operation that results in a number beyond the bounds of - the integer type, a float will be returned - instead. + + + + + - - + + Integer overflow + + + If you specify a number beyond the bounds of the integer type, + it will be interpreted as a float instead. Also, if you perform + an operation that results in a number beyond the bounds of the + integer type, a float will be returned instead. + + + ]]> - - - - - Unfortunately, there was a bug in PHP so that this - does not always work correctly when there are negative numbers - involved. For example: when you do -50000 * - $million, the result will be - -429496728. However, when both operands are - positive there is no problem. - - - This is solved in PHP 4.1.0. - - - - - There is no integer division operator in PHP. - 1/2 yields the float - 0.5. You can cast the value to - an integer to always round it downwards, or you can - use the round function. - - + + + + + + Unfortunately, there was a bug in PHP so that this does not always work + correctly when there are negative numbers involved. For example: when you + do -50000 * $million, the result will be + -429496728. However, when both operands are positive + there is no problem. + + + + This is solved in PHP 4.1.0. + + + + + + There is no integer division operator in PHP. 1/2 yields + the float 0.5. You can cast the value to an + integer to always round it downwards, or you can use the + round function. + + + ]]> - - - - + + + + + + + Converting to integer + + + To explicitly convert a value to integer, use either the + (int) or the (integer) cast. However, + in most cases you do not need to use the cast, since a value will be + automatically converted if an operator, function or control structure + requires an integer argument. You can also convert a value to + integer with the function intval. + + + + See also type-juggling. + + + From <link linkend="language.types.boolean">booleans</link> - - Converting to integer - - To explicitly convert a value to integer, use either - the (int) or the (integer) cast. - However, in most cases you do not need to use the cast, since a value - will be automatically converted if an operator, function or - control structure requires an integer argument. - You can also convert a value to integer with the function - intval. - - - See also type-juggling. - - - - From <link linkend="language.types.boolean" - >booleans</link> - - &false; will yield - 0 (zero), and &true; - will yield 1 (one). - - + + &false; will yield 0 (zero), and &true; will yield + 1 (one). + + - - From <link linkend="language.types.float">floating point numbers</link> - - When converting from float to integer, the number will - be rounded towards zero. - - - - If the float is beyond the boundaries of integer - (usually +/- 2.15e+9 = 2^31), - the result is undefined, since the float hasn't - got enough precision to give an exact integer result. - No warning, not even a notice will be issued in this - case! - - - - Never cast an unknown fraction to integer, as this can - sometimes lead to unexpected results. - - + + + From <link linkend="language.types.float">floating point + numbers</link> + + + + When converting from float to integer, the number will be rounded towards zero. + + + + If the float is beyond the boundaries of integer (usually + +/- 2.15e+9 = 2^31), the result is undefined, since the + float hasn't got enough precision to give an exact integer result. No + warning, not even a notice will be issued in this case! + + + + + Never cast an unknown fraction to integer, as this can + sometimes lead to unexpected results. + + + ]]> - - - - See for more information the warning - about float-precision. - - - - - From strings - - See String - conversion to numbers - - - - - From other types - - - - Behaviour of converting to integer is undefined for other - types. Currently, the behaviour is the same as if the value - was first converted to boolean. However, do - not rely on this behaviour, as it can - change without notice. - - - - - - + + + + See for more information the warning + about float-precision. + + + + + + From strings + + + See String conversion to + numbers + + + + + From other types + + + + + Behaviour of converting to integer is undefined for other types. + Currently, the behaviour is the same as if the value was first + converted to + boolean. However, do not rely on this + behaviour, as it can change without notice. + + + + + + + - - NULL - - - The special &null; value represents - that a variable has no value. &null; is the only possible value of type - NULL. - - - - The null type was introduced in PHP 4. - - + + + NULL + + + The special &null; value represents that a variable has no value. &null; is + the only possible value of type NULL. + + + + + The null type was introduced in PHP 4. + + + + + A variable is considered to be &null; if + + + - A variable is considered to be &null; if - - - - it has been assigned the constant &null;. - - - - - it has not been set to any value yet. - - - - - it has been unset. - - - + it has been assigned the constant &null;. - - - Syntax + + - There is only one value of type &null;, and that is - the case-insensitive keyword &null;. - - + it has not been set to any value yet. + + + + + it has been unset. + + + + + + + Syntax + + + There is only one value of type &null;, and that is the case-insensitive + keyword &null;. + + + ]]> - - - - - See also is_null and unset. - - - + + + + + + See also is_null and unset. + + + + - - Objects + + + Objects - - Object Initialization + + Object Initialization - - To initialize an object, you use the new - statement to instantiate the object to a variable. + + To initialize an object, you use the new statement to + instantiate the object to a variable. - - + + do_foo(); ?> ]]> - - - - - For a full discussion, please read the section Classes and Objects. - - - - - Converting to object - - - If an object is converted to an object, it is not modified. If a value - of any other type is converted to an object, a new instance of the - stdClass built in class is created. If the value - was &null;, the new instance will be empty. Array converts to an object - with properties named by array keys and with corresponding values. For - any other value, a member variable named scalar will - contain the value. - - + + + + + + For a full discussion, please read the section + Classes and Objects. + + + + + Converting to object + + + If an object is converted to an object, it is not modified. If a value of any + other type is converted to an object, a new instance of the + stdClass built in class is created. If the value was + &null;, the new instance will be empty. Array converts to an object with + properties named by array keys and with corresponding values. For any other + value, a member variable named scalar will contain the + value. + + + scalar; // outputs 'ciao' ?> ]]> - - - - - - + + + + + + - - Pseudo-types and variables used in this documentation + + + Pseudo-types and variables used in this documentation - - mixed - - mixed indicates that a parameter may accept multiple (but not - necessarily all) types. - - - gettype for example will accept all PHP types, - while str_replace will accept strings and arrays. - - - - - number - - number indicates that a parameter can be either - integer or float. - - + + mixed - - callback - - Some functions like call_user_func - or usort accept user defined - callback functions as a parameter. Callback functions can not only - be simple functions but also object methods including static class - methods. - - - A PHP function is simply passed by its name as a string. You can - pass any built-in or user defined function. Note that language - constructs like - array, - echo, - empty, - eval, - exit, - isset, - list, - print or - unset cannot be called using a callback. - - - A method of an instantiated object is passed as an array containing - an object as the element with index 0 and a method name as the - element with index 1. - - - Static class methods can also be passed without instantiating an - object of that class by passing the class name instead of an - object as the element with index 0. - - - Apart from common user-defined function, - create_function can be used to create an anonymous - callback function. - + + mixed indicates that a parameter may accept multiple (but + not necessarily all) types. + - - - - Callback function examples - - + + gettype for example will accept all PHP types, while + str_replace will accept strings and arrays. + + + + + number + + + number indicates that a parameter can be either + integer or float. + + + + + callback + + + Some functions like call_user_func or + usort accept user defined callback functions as a + parameter. Callback functions can not only be simple functions but also + object methods including static class methods. + + + + A PHP function is simply passed by its name as a string. You can pass any + built-in or user defined function. Note that language constructs like + array, echo, + empty, eval, + exit, isset, + list, print or + unset cannot be called using a callback. + + + + A method of an instantiated object is passed as an array containing an object + as the element with index 0 and a method name as the element with index 1. + + + + Static class methods can also be passed without instantiating an object of + that class by passing the class name instead of an object as the element with + index 0. + + + + Apart from common user-defined function, create_function + can be used to create an anonymous callback function. + + + + + + Callback function examples + + ]]> - - - - - - In PHP4, you will have to use a reference to create a callback that - points to the actual object, and not a copy of it. For more details, - see References Explained. - - + + + - - - - void - - void in return type means that the return value is - useless. void in parameters list means that the - function doesn't accept any parameters. - - + + + In PHP4, you will have to use a reference to create a callback that points + to the actual object, and not a copy of it. For more details, see + References Explained. + + - - ... - - $... in function prototypes means - and so on. - This variable name is used when a function can take an endless number of - arguments. - - - + + + + void + + + void in return type means that the return value is + useless. void in parameters list means that the function + doesn't accept any parameters. + + + + + ... + + + $... in function prototypes means + and so on. This variable name is used when a function can + take an endless number of arguments. + + + + - - Resource - - - A resource is a special variable, holding - a reference to an external resource. Resources - are created and used by special functions. - See the appendix - for a listing of all these - functions and the corresponding resource types. - - - - - The resource type was introduced in PHP 4 - - + + + Resource + + + A resource is a special variable, holding a reference to an external resource. + Resources are created and used by special functions. See the + appendix for a listing of all these functions + and the corresponding resource types. + + + + + The resource type was introduced in PHP 4 + + - - See also get_resource_type. - + + See also get_resource_type. + - - Converting to resource - - - As resource types hold special handlers to opened - files, database connections, image canvas areas and - the like, you cannot convert any value to a resource. - - + + Converting to resource + + + As resource types hold special handlers to opened files, database + connections, image canvas areas and the like, you cannot convert any value to + a resource. + + - - Freeing resources - - - Due to the reference-counting system introduced - with PHP 4's Zend Engine, it is automatically detected - when a resource is no longer referred to (just - like Java). When this is - the case, all resources that were in use for this - resource are made free by the garbage collector. - For this reason, it is rarely ever necessary to - free the memory manually by using some free_result - function. - - - Persistent database links are special, they - are not destroyed by the - garbage collector. See also the section about persistent - connections. - - - - - - + + Freeing resources + + + Due to the reference-counting system introduced with PHP 4's Zend Engine, it + is automatically detected when a resource is no longer referred to (just like + Java). When this is the case, all resources that were in use for this resource + are made free by the garbage collector. For this reason, it is rarely ever + necessary to free the memory manually by using some free_result function. + + + + Persistent database links are special, they are not + destroyed by the garbage collector. See also the section about + persistent + connections. + + + + + + - - Strings + + + Strings + + + A string is series of characters. In PHP, a character is the same + as a byte, that is, there are exactly 256 different characters possible. This + also implies that PHP has no native support of Unicode. See + utf8_encode and utf8_decode for some + Unicode support. + + + + + It is no problem for a string to become very large. There is no practical + bound to the size of strings imposed by PHP, so there is no reason at all to + worry about long strings. + + + + + Syntax + + + A string literal can be specified in three different ways. + + + + + single quoted + + + + + double quoted + + + + + heredoc syntax + + + + + + + Single quoted + - A string is series of characters. In PHP, - a character is the same as a byte, that is, there are exactly - 256 different characters possible. This also implies that PHP - has no native support of Unicode. See utf8_encode - and utf8_decode for some Unicode support. + The easiest way to specify a simple string is to enclose it in single quotes + (the character '). - - - It is no problem for a string to become very large. - There is no practical bound to the size - of strings imposed by PHP, so there is no reason at all - to worry about long strings. - - - - Syntax - - A string literal can be specified in three different - ways. - - - - single quoted - - - - - double quoted - - - - - heredoc syntax - - + + To specify a literal single quote, you will need to escape it with a + backslash (\), like in many other languages. If a + backslash needs to occur before a single quote or at the end of the string, + you need to double it. Note that if you try to escape any other character, + the backslash will also be printed! So usually there is no need to escape + the backslash itself. - - - - Single quoted - - The easiest way to specify a simple string is to - enclose it in single quotes (the character '). - - - To specify a literal single - quote, you will need to escape it with a backslash - (\), like in many other languages. - If a backslash needs to occur before a single quote or at - the end of the string, you need to double it. - Note that if you try to escape any - other character, the backslash will also be printed! So - usually there is no need to escape the backslash itself. - - - In PHP 3, a warning will - be issued at the E_NOTICE level when this - happens. - - - - - Unlike the two other syntaxes, variables and escape sequences - for special characters will not be expanded - when they occur in single quoted strings. - - - - + + + In PHP 3, a warning will be issued at the E_NOTICE + level when this happens. + + + + + + Unlike the two other syntaxes, + variables and escape sequences + for special characters will not be expanded when they + occur in single quoted strings. + + + + + ]]> - - - - - - Double quoted - - If the string is enclosed in double-quotes ("), - PHP understands more escape sequences for special - characters: - - - Escaped characters - - - - sequence - meaning - - - - - \n - linefeed (LF or 0x0A (10) in ASCII) - - - \r - carriage return (CR or 0x0D (13) in ASCII) - - - \t - horizontal tab (HT or 0x09 (9) in ASCII) - - - \v - vertical tab (VT or 0x0B (11) in ASCII) (since PHP 5.2.5) - - - \f - form feed (FF or 0x0C (12) in ASCII) (since PHP 5.2.5) - - - \\ - backslash - - - \$ - dollar sign - - - \" - double-quote - - - \[0-7]{1,3} - - the sequence of characters matching the regular - expression is a character in octal notation - - - - \x[0-9A-Fa-f]{1,2} - - the sequence of characters matching the regular - expression is a character in hexadecimal notation - - - - -
- - Again, if you try to escape any other character, the - backslash will be printed too! - Before PHP 5.1.1, backslash in \{$var} hasn't been - printed. - - - But the most important feature of double-quoted strings - is the fact that variable names will be expanded. - See string - parsing for details. - - - - - Heredoc - - Another way to delimit strings is by using heredoc syntax - ("<<<"). One should provide an identifier (followed by new line) after - <<<, then the string, and then the - same identifier to close the quotation. - - - The closing identifier must begin in the - first column of the line. Also, the identifier used must follow - the same naming rules as any other label in PHP: it must contain - only alphanumeric characters and underscores, and must start with - a non-digit character or underscore. - - - - - It is very important to note that the line with the closing - identifier contains no other characters, except - possibly a semicolon (;). - That means especially that the identifier - may not be indented, and there - may not be any spaces or tabs after or before the semicolon. - It's also important to realize that the first character before - the closing identifier must be a newline as defined by your - operating system. This is \r on Macintosh - for example. Closing delimiter (possibly followed by a semicolon) must - be followed by a newline too. - - - If this rule is broken and the closing identifier is not "clean" - then it's not considered to be a closing identifier and PHP - will continue looking for one. If in this case a proper closing - identifier is not found then a parse error will result with the - line number being at the end of the script. - - - It is not allowed to use heredoc syntax in initializing class members. - Use other string syntaxes instead. - - Invalid example - + + + + + + + + Double quoted + + + If the string is enclosed in double-quotes ("), + PHP understands more escape sequences for special + characters: + + + + Escaped characters + + + + + sequence + meaning + + + + + + \n + linefeed (LF or 0x0A (10) in ASCII) + + + \r + carriage return (CR or 0x0D (13) in ASCII) + + + \t + horizontal tab (HT or 0x09 (9) in ASCII) + + + \v + vertical tab (VT or 0x0B (11) in ASCII) (since PHP 5.2.5) + + + \f + form feed (FF or 0x0C (12) in ASCII) (since PHP 5.2.5) + + + \\ + backslash + + + \$ + dollar sign + + + \" + double-quote + + + \[0-7]{1,3} + + the sequence of characters matching the regular expression is a + character in octal notation + + + + \x[0-9A-Fa-f]{1,2} + + the sequence of characters matching the regular expression is a + character in hexadecimal notation + + + + +
+ + + Again, if you try to escape any other character, the backslash will be + printed too! Before PHP 5.1.1, backslash in \{$var} + hasn't been printed. + + + + But the most important feature of double-quoted strings is the fact that + variable names will be expanded. See + string parsing for + details. + + + + + Heredoc + + + Another way to delimit strings is by using heredoc syntax ("<<<"). + One should provide an identifier (followed by new line) after + <<<, then the string, and then the same + identifier to close the quotation. + + + + The closing identifier must begin in the first column + of the line. Also, the identifier used must follow the same naming rules as + any other label in PHP: it must contain only alphanumeric characters and + underscores, and must start with a non-digit character or underscore. + + + + + It is very important to note that the line with the closing identifier + contains no other characters, except possibly a + semicolon (;). That means especially that the identifier + may not be indented, and there may not be any spaces + or tabs after or before the semicolon. It's also important to realize that + the first character before the closing identifier must be a newline as + defined by your operating system. This is \r on + Macintosh for example. Closing delimiter (possibly followed by a semicolon) + must be followed by a newline too. + + + + If this rule is broken and the closing identifier is not "clean" then it's + not considered to be a closing identifier and PHP will continue looking for + one. If in this case a proper closing identifier is not found then a parse + error will result with the line number being at the end of the script. + + + + It is not allowed to use heredoc syntax in initializing class members. Use + other string syntaxes instead. + + + Invalid example + ]]> - - - - + + + + - - Heredoc text behaves just like a double-quoted string, without - the double-quotes. This means that you do not need to escape quotes - in your here docs, but you can still use the escape codes listed - above. Variables are expanded, but the same care must be taken - when expressing complex variables inside a heredoc as with - strings. - - Heredoc string quoting example - + + Heredoc text behaves just like a double-quoted string, without the + double-quotes. This means that you do not need to escape quotes in your here + docs, but you can still use the escape codes listed above. Variables are + expanded, but the same care must be taken when expressing complex variables + inside a heredoc as with strings. + + + Heredoc string quoting example + ]]> - - - - - - - Heredoc support was added in PHP 4. - - - + + + - - Variable parsing - - When a string is specified in double quotes or with - heredoc, variables are - parsed within it. - - - There are two types of syntax: a - simple - one and a - complex - one. - The simple syntax is the most common and convenient. It provides a way - to parse a variable, an array value, or an - object property. - - - The complex syntax was introduced in PHP 4, and can be recognised - by the curly braces surrounding the expression. - + + + Heredoc support was added in PHP 4. + + + - - Simple syntax - - If a dollar sign ($) is encountered, the - parser will greedily take as many tokens as possible to form a - valid variable name. Enclose the variable name in curly - braces if you want to explicitly specify the end of the name. - - - + + Variable parsing + + + When a string is specified in double quotes or with heredoc, + variables are parsed within it. + + + + There are two types of syntax: a + simple one and a + complex one. + The simple syntax is the most common and convenient. It provides a way to + parse a variable, an array value, or an object + property. + + + + The complex syntax was introduced in PHP 4, and can be recognised by the + curly braces surrounding the expression. + + + + Simple syntax + + + If a dollar sign ($) is encountered, the parser will + greedily take as many tokens as possible to form a valid variable name. + Enclose the variable name in curly braces if you want to explicitly specify + the end of the name. + + + + ]]> - - - - Similarly, you can also have an array index or an - object property parsed. With array indices, the closing square - bracket (]) marks the end of the index. For - object properties the same rules apply as to simple variables, - though with object properties there doesn't exist a trick like - the one with variables. - - - - - - + + + + + Similarly, you can also have an array index or an + object property parsed. With array indices, the closing square + bracket (]) marks the end of the index. For object + properties the same rules apply as to simple variables, though with object + properties there doesn't exist a trick like the one with variables. + + + + + + {width}00 centimeters broad."; // XXX: like the $obj->{expr} syntax outside a string works, // XXX: analogously to the ${expr} syntax for variable var's. --> - - - - For anything more complex, you should use the complex syntax. - - + + - - Complex (curly) syntax - - This isn't called complex because the syntax is complex, - but because you can include complex expressions this way. - - - In fact, you can include any value that is in the namespace - in strings with this syntax. You simply write the expression - the same way as you would outside the string, and then include - it in { and }. Since you can't escape '{', this syntax will - only be recognised when the $ is immediately following the {. - (Use "{\$" to get a literal "{$"). - Some examples to make it clear: - - - + + For anything more complex, you should use the complex syntax. + + + + + Complex (curly) syntax + + + This isn't called complex because the syntax is complex, but because you + can include complex expressions this way. + + + + In fact, you can include any value that is in the namespace in strings with + this syntax. You simply write the expression the same way as you would + outside the string, and then include it in { and }. Since you can't escape + '{', this syntax will only be recognised when the $ is immediately following + the {. (Use "{\$" to get a literal "{$"). Some examples to make it clear: + + + + getNam $beer = 'Heineken'; echo "I'd like to have another {${ strrev('reeb') }}, hips"; --> - - - - - - Functions and method calls inside {$ } work since PHP 5. - - - - - Parsing variables within strings uses more memory than string - concatenation. When writing a PHP script in which memory usage is a - concern, consider using the concatenation operator (.) rather than - variable parsing. - - - - + + - - String access and modification by character + - Characters within strings may be accessed and modified by specifying the - zero-based offset of the desired character after the string - using square array-brackets like $str[42] so think of - a string as an array of characters. + Functions and method calls inside {$ } work since PHP 5. - - - They may also be accessed using braces like $str{42} - for the same purpose. However, using square array-brackets is preferred - because the {braces} style is deprecated as of PHP 6. - - + + + - - Some string examples - + Parsing variables within strings uses more memory than string + concatenation. When writing a PHP script in which memory usage is a + concern, consider using the concatenation operator (.) rather than + variable parsing. + + + + + + + String access and modification by character + + + Characters within strings may be accessed and modified by specifying the + zero-based offset of the desired character after the string using square + array-brackets like $str[42] so think of a string as an + array of characters. + + + + + They may also be accessed using braces like $str{42} for + the same purpose. However, using square array-brackets is preferred because + the {braces} style is deprecated as of PHP 6. + + + + + + + Some string examples + ]]> - - - - - - Accessing by [] or {} to - variables of other type silently returns &null;. - - - + + + - + + + Accessing by [] or {} to + variables of other type silently returns &null;. + + + - - Useful functions and operators - - Strings may be concatenated using the '.' (dot) operator. Note - that the '+' (addition) operator will not work for this. Please - see String - operators for more information. - - - There are a lot of useful functions for string modification. - - - See the string functions section - for general functions, the regular expression functions for - advanced find&replacing (in two tastes: - Perl and - POSIX extended). - - - There are also functions for URL-strings, - and functions to encrypt/decrypt strings - (mcrypt and - mhash). - - - Finally, if you still didn't find what you're looking for, - see also the character type functions. - - + - - Converting to string - - - You can convert a value to a string using the (string) - cast, or the strval function. String conversion - is automatically done in the scope of an expression for you where a - string is needed. This happens when you use the echo - or print functions, or when you compare a variable - value to a string. Reading the manual sections on Types and Type Juggling will make - the following clearer. See also settype. - - - - A boolean &true; value is converted to the string "1", - the &false; value is represented as "" (empty string). - This way you can convert back and forth between boolean and string values. - - - An integer or a floating point number (float) - is converted to a string representing the number with its digits - (including the exponent part for floating point numbers). - Floating point numbers can be converted using the exponential notation - (4.1E+6). - - - - The decimal point character is defined in the script's - locale (category LC_NUMERIC). - See setlocale. - - - - Arrays are always converted to the string "Array", - so you cannot dump out the contents of an array with - echo or print to see what is inside - them. To view one element, you'd do something like - echo $arr['foo']. See below for tips on dumping/viewing the - entire contents. - - - Objects in PHP 4 are always converted to the string "Object". - If you would like to print out the member variable values of an - object for debugging reasons, read the paragraphs - below. If you would like to find out the class name of which an object - is an instance of, use get_class. - As of PHP 5, __toString() method is used if applicable. - - - Resources are always converted to strings with the structure - "Resource id #1" where 1 is - the unique number of the resource assigned by PHP during runtime. - If you would like to get the type of the resource, use - get_resource_type. - - - &null; is always converted to an empty string. - - - - As you can see above, printing out the arrays, objects or resources does not - provide you any useful information about the values themselves. Look at the - functions print_r and var_dump - for better ways to print out values for debugging. - - - - You can also convert PHP values to strings to store them permanently. This - method is called serialization, and can be done with the function - serialize. You can also serialize PHP values to - XML structures, if you have WDDX support - in your PHP setup. - - + + Useful functions and operators - - String conversion to numbers + + Strings may be concatenated using the '.' (dot) operator. Note that the '+' + (addition) operator will not work for this. Please see + String operators for more + information. + - - When a string is evaluated as a numeric value, the resulting - value and type are determined as follows. - - - The string will evaluate as a float if it contains any of the - characters '.', 'e', or 'E'. Otherwise, it will evaluate as an - integer. - - - The value is given by the initial portion of the string. If the - string starts with valid numeric data, this will be the value - used. Otherwise, the value will be 0 (zero). Valid numeric data - is an optional sign, followed by one or more digits (optionally - containing a decimal point), followed by an optional - exponent. The exponent is an 'e' or 'E' followed by one or more - digits. - - - + + There are a lot of useful functions for string modification. + + + + See the string functions section for + general functions, the regular expression functions for advanced find & + replacing (in two tastes: Perl and + POSIX extended). + + + + There are also functions for URL-strings, and + functions to encrypt/decrypt strings + (mcrypt and + mhash). + + + + Finally, if you still didn't find what you're looking for, see also the + character type functions. + + + + + Converting to string + + + You can convert a value to a string using the (string) + cast, or the strval function. String conversion is + automatically done in the scope of an expression for you where a string is + needed. This happens when you use the echo or + print functions, or when you compare a variable value to + a string. Reading the manual sections on + Types and + Type Juggling will make + the following clearer. See also settype. + + + + A boolean &true; value is converted to the string + "1", the &false; value is represented as + "" (empty string). This way you can convert back and forth + between boolean and string values. + + + + An integer or a floating point number (float) is + converted to a string representing the number with its digits (including the + exponent part for floating point numbers). Floating point numbers can be + converted using the exponential notation (4.1E+6). + + + + + The decimal point character is defined in the script's locale (category + LC_NUMERIC). See setlocale. + + + + + Arrays are always converted to the string "Array", so you + cannot dump out the contents of an array with + echo or print to see what is inside + them. To view one element, you'd do something like + echo $arr['foo']. See below for tips on dumping/viewing + the entire contents. + + + + Objects in PHP 4 are always converted to the string + "Object". If you would like to print out the member + variable values of an object for debugging reasons, read the + paragraphs below. If you would like to find out the class name of which an + object is an instance of, use get_class. As of PHP 5, + __toString() method is used if applicable. + + + + Resources are always converted to strings with the structure + "Resource id #1" where 1 is the unique + number of the resource assigned by PHP during runtime. If you + would like to get the type of the resource, use + get_resource_type. + + + + &null; is always converted to an empty string. + + + + As you can see above, printing out the arrays, objects or resources does not + provide you any useful information about the values themselves. Look at the + functions print_r and var_dump for + better ways to print out values for debugging. + + + + You can also convert PHP values to strings to store them permanently. This + method is called serialization, and can be done with the function + serialize. You can also serialize PHP values to XML + structures, if you have WDDX support in your + PHP setup. + + + + + String conversion to numbers + + + When a string is evaluated as a numeric value, the resulting value and type + are determined as follows. + + + + The string will evaluate as a float if it contains any of the + characters '.', 'e', or 'E'. Otherwise, it will evaluate as an integer. + + + + The value is given by the initial portion of the string. If the string starts + with valid numeric data, this will be the value used. Otherwise, the value + will be 0 (zero). Valid numeric data is an optional sign, followed by one or + more digits (optionally containing a decimal point), followed by an optional + exponent. The exponent is an 'e' or 'E' followed by one or more digits. + + + + ]]> - - - - For more information on this conversion, see the Unix manual page - for strtod(3). - - - If you would like to test any of the examples in this section, - you can cut and paste the examples and insert the following line - to see for yourself what's going on: - - + + + + + For more information on this conversion, see the Unix manual page for + strtod(3). + + + + If you would like to test any of the examples in this section, you can cut + and paste the examples and insert the following line to see for yourself + what's going on: + + + \n"; ?> ]]> - - - - - Do not expect to get the code of one character by converting it - to integer (as you would do in C for example). Use the functions - ord and chr to convert - between charcodes and characters. - + + + - - + + Do not expect to get the code of one character by converting it to integer + (as you would do in C for example). Use the functions + ord and chr to convert between + charcodes and characters. + + + + - - Type Juggling + + + Type Juggling - - PHP does not require (or support) explicit type definition in - variable declaration; a variable's type is determined by the - context in which that variable is used. That is to say, if you - assign a string value to variable $var, - $var becomes a string. If you then assign an - integer value to $var, it becomes an - integer. - - - An example of PHP's automatic type conversion is the addition - operator '+'. If any of the operands is a float, then all - operands are evaluated as floats, and the result will be a - float. Otherwise, the operands will be interpreted as integers, - and the result will also be an integer. Note that this does NOT - change the types of the operands themselves; the only change is in - how the operands are evaluated. - - + + PHP does not require (or support) explicit type definition in variable + declaration; a variable's type is determined by the context in which that + variable is used. That is to say, if you assign a string value to variable + $var, $var becomes a string. If + you then assign an integer value to $var, it becomes an + integer. + + + + An example of PHP's automatic type conversion is the addition operator '+'. + If any of the operands is a float, then all operands are evaluated as floats, + and the result will be a float. Otherwise, the operands will be interpreted as + integers, and the result will also be an integer. Note that this does NOT + change the types of the operands themselves; the only change is in how the + operands are evaluated. + + + - - - - - If the last two examples above seem odd, see String - conversion to numbers. - - - If you wish to force a variable to be evaluated as a certain type, - see the section on Type - casting. If you wish to change the type of a variable, see - settype. - - - If you would like to test any of the examples in this section, you - can use the var_dump function. - - - - The behaviour of an automatic conversion to array is currently - undefined. - - - Also, because PHP supports indexing into strings via offsets using - the same syntax as array indexing, the following example holds true - for all PHP versions: - - + + + + + + If the last two examples above seem odd, see + String conversion to + numbers. + + + + If you wish to force a variable to be evaluated as a certain type, see the + section on Type casting. If + you wish to change the type of a variable, see settype. + + + If you would like to test any of the examples in this section, you + can use the var_dump function. + + + + + The behaviour of an automatic conversion to array is currently undefined. + + + + Also, because PHP supports indexing into strings via offsets using the same + syntax as array indexing, the following example holds true for all PHP + versions: + + + ]]> - - - - - See the section titled String - access by character for more information. - - + + + - - Type Casting + + See the section titled String + access by character for more information. + + - - Type casting in PHP works much as it does in C: the name of the - desired type is written in parentheses before the variable which - is to be cast. - - + + Type Casting + + + Type casting in PHP works much as it does in C: the name of the desired type + is written in parentheses before the variable which is to be cast. + + + ]]> - - - - - The casts allowed are: - - - (int), (integer) - cast to integer - - - (bool), (boolean) - cast to boolean - - - (float), (double), (real) - cast to float - - - (string) - cast to string - - - (binary) - cast to binary string (PHP 6) - - - (array) - cast to array - - - (object) - cast to object - - - - - (binary) casting and b prefix forward support was added in PHP 5.2.1 - - - Note that tabs and spaces are allowed inside the parentheses, so - the following are functionally equivalent: - - + + + + + + The casts allowed are: + + + + (int), (integer) - cast to integer + + + (bool), (boolean) - cast to boolean + + + (float), (double), (real) - cast to float + + + (string) - cast to string + + + (binary) - cast to binary string (PHP 6) + + + (array) - cast to array + + + (object) - cast to object + + + + + + (binary) casting and b prefix forward support was added in PHP 5.2.1 + + + + Note that tabs and spaces are allowed inside the parentheses, so the + following are functionally equivalent: + + + ]]> - - - Casting a literal strings and variables to binary strings: - - + + + + Casting a literal strings and variables to binary strings: + + + ]]> - - - - - - Instead of casting a variable to string, you can also enclose - the variable in double quotes. - - + + + + + + + Instead of casting a variable to string, you can also enclose + the variable in double quotes. + + + ]]> - - - - - - - It may not be obvious exactly what will happen when casting - between certain types. For more info, see these sections: - - - - Converting to - boolean - - - Converting to - integer - - - Converting to - float - - - Converting to - string - - - Converting to - array - - - Converting to - object - - - Converting to - resource - - - - - The type comparison tables - - - - - - + + + + + + + It may not be obvious exactly what will happen when casting between certain + types. For more info, see these sections: + + + + Converting to + boolean + + + Converting to + integer + + + Converting to + float + + + Converting to + string + + + Converting to + array + + + Converting to + object + + + Converting to + resource + + + + + The type comparison tables + + + + + + +