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Function functions, aggregated from misc/variables

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Ron Chmara 2000-09-07 05:11:27 +00:00
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functions/funchand.xml Executable file
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<reference id="ref.funchand">
<title>Function Handling functions</title>
<titleabbrev>Functions</titleabbrev>
<partintro>
<para>
These functions all handle various operations involved in working
with functions.
</para>
</partintro>
<refentry id="function.call-user-func">
<refnamediv>
<refname>call_user_func</refname>
<refpurpose>
Call a user function given by the first parameter
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>mixed
<function>call_user_func</function>
</funcdef>
<paramdef>string
<parameter>function_name</parameter>
</paramdef>
<paramdef>mixed
<parameter><optional>parameter</optional></parameter>
</paramdef>
<paramdef>mixed
<parameter><optional>...</optional></parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
<para>
Call a user defined function given by the
<parameter>function_name</parameter> parameter. Take the
following:
<informalexample>
<programlisting role="php">
function barber ($type) {
print "You wanted a $type haircut, no problem";
}
call_user_func ('barber', "mushroom");
call_user_func ('barber', "shave");
</programlisting>
</informalexample>
</para>
</refsect1>
</refentry>
<refentry id="function.create-function">
<refnamediv>
<refname>create_function</refname>
<refpurpose>Create an anonymous (lambda-style) function</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>string <function>create_function</function></funcdef>
<paramdef>string <parameter>args</parameter></paramdef>
<paramdef>string <parameter>code</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>
Creates an anonymous function from the parameters passed, and
returns a unique name for it. Usually the
<parameter>args</parameter> will be passed as a single quote
delimited string, and this is also recommended for the
<parameter>code</parameter>. The reason for using single quoted
strings, is to protect
the variable names from parsing, otherwise, if you use double
quotes there will be a need to escape the variable names, e.g.
<literal>\$avar</literal>.
</para>
<para>
You can use this function, to (for example) create a function
from information gathered at run time:
<example>
<title>
Creating an anonymous function with <function>create_function</function>
</title>
<programlisting role="php">
$newfunc = create_function('$a,$b','return "ln($a) + ln($b) = ".log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2,M_E)."\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
</programlisting>
</example>
Or, perhaps to have general handler function that can apply a set
of operations to a list of parameters:
<example>
<title>
Making a general processing function with
<function>create_function</function>
</title>
<programlisting role="php">
function process($var1, $var2, $farr) {
for ($f=0; $f &lt; count($farr); $f++)
echo $farr[$f]($var1,$var2)."\n";
}
// create a bunch of math functions
$f1 = 'if ($a &gt;=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}';
$f2 = "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);";
$f3 = 'if ($a &gt; 0 &amp;&amp; $b != 0) {return "ln(a)/b = ".log($a)/$b;} else {return false;}';
$farr = array(
create_function('$x,$y', 'return "some trig: ".(sin($x) + $x*cos($y));'),
create_function('$x,$y', 'return "a hypotenuse: ".sqrt($x*$x + $y*$y);'),
create_function('$a,$b', $f1),
create_function('$a,$b', $f2),
create_function('$a,$b', $f3)
);
echo "\nUsing the first array of anonymous functions\n";
echo "parameters: 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);
// now make a bunch of string processing functions
$garr = array(
create_function('$b,$a','if (strncmp($a,$b,3) == 0) return "** \"$a\" '.
'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";'),
create_function('$a,$b','; return "CRCs: ".crc32($a)." , ".crc32(b);'),
create_function('$a,$b','; return "similar(a,b) = ".similar_text($a,$b,&$p)."($p%)";')
);
echo "\nUsing the second array of anonymous functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
</programlisting>
</example>
and when you run the code above, the output will be:
<informalexample>
<programlisting>
Using the first array of anonymous functions
parameters: 2.3445, M_PI
some trig: -1.6291725057799
a hypotenuse: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a/b) = 0.27122299212594
Using the second array of anonymous functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: -725381282 , 1908338681
similar(a,b) = 11(45.833333333333%)
</programlisting>
</informalexample>
But perhaps the most common use for of lambda-style (anonymous) functions
is to create callback functions, for example when using
<function>array_walk</function> or <function>usort</function>
<example>
<title>Using anonymous functions as callback functions</title>
<programlisting role="php">
$av = array("the ","a ","that ","this ");
array_walk($av, create_function('&$v,$k','$v = $v."mango";'));
print_r($av); // for PHP3 use var_dump()
// outputs:
// Array
// (
// [0] =&gt; the mango
// [1] =&gt; a mango
// [2] =&gt; that mango
// [3] =&gt; this mango
// )
// an array of strings ordered from shorter to longer
$sv = array("small","larger","a big string","it is a string thing");
print_r($sv);
// outputs:
// Array
// (
// [0] =&gt; small
// [1] =&gt; larger
// [2] =&gt; a big string
// [3] =&gt; it is a string thing
// )
// sort it from longer to shorter
usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);
// outputs:
// Array
// (
// [0] =&gt; it is a string thing
// [1] =&gt; a big string
// [2] =&gt; larger
// [3] =&gt; small
// )
</programlisting>
</example>
</para>
</refsect1>
</refentry>
<refentry id="function.func-get-arg">
<refnamediv>
<refname>func_get_arg</refname>
<refpurpose>Return an item from the argument list</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>mixed <function>func_get_arg</function></funcdef>
<paramdef>int <parameter>arg_num</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<simpara>
Returns the argument which is at the
<parameter>arg_num</parameter>'th offset into a user-defined
function's argument list. Function arguments are counted starting
from zero. <function>Func_get_arg</function> will generate a
warning if called from outside of a function definition.
</simpara>
<simpara>
If <parameter>arg_num</parameter> is greater than the number of
arguments actually passed, a warning will be generated and
<function>func_get_arg</function> will return FALSE.
</simpara>
<para>
<informalexample>
<programlisting role="php">
&lt;?php
function foo() {
$numargs = func_num_args();
echo "Number of arguments: $numargs&lt;br&gt;\n";
if ($numargs &gt;= 2) {
echo "Second argument is: " . func_get_arg (1) . "&lt;br&gt;\n";
}
}
foo (1, 2, 3);
?&gt;
</programlisting>
</informalexample>
</para>
<simpara>
<function>Func_get_arg</function> may be used in conjunction with
<function>func_num_args</function> and
<function>func_get_args</function> to allow user-defined
functions to accept variable-length argument lists.
</simpara>
<note>
<simpara>
This function was added in PHP 4.
</simpara>
</note>
</refsect1>
</refentry>
<refentry id="function.func-get-args">
<refnamediv>
<refname>func_get_args</refname>
<refpurpose>
Returns an array comprising a function's argument list
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>array <function>func_get_args</function></funcdef>
<paramdef>void <parameter></parameter></paramdef>
</funcprototype>
</funcsynopsis>
<simpara>
Returns an array in which each element is the corresponding
member of the current user-defined function's argument
list. <function>Func_get_args</function> will generate a warning
if called from outside of a function definition.
</simpara>
<para>
<informalexample>
<programlisting role="php">
&lt;?php
function foo() {
$numargs = func_num_args();
echo "Number of arguments: $numargs&lt;br&gt;\n";
if ($numargs &gt;= 2) {
echo "Second argument is: " . func_get_arg (1) . "&lt;br&gt;\n";
}
$arg_list = func_get_args();
for ($i = 0; $i &lt; $numargs; $i++) {
echo "Argument $i is: " . $arg_list[$i] . "&lt;br&gt;\n";
}
}
foo (1, 2, 3);
?&gt;
</programlisting>
</informalexample>
</para>
<simpara>
<function>Func_get_args</function> may be used in conjunction
with <function>func_num_args</function> and
<function>func_get_arg</function> to allow user-defined functions
to accept variable-length argument lists.
</simpara>
<note>
<simpara>
This function was added in PHP 4.
</simpara>
</note>
</refsect1>
</refentry>
<refentry id="function.func-num-args">
<refnamediv>
<refname>func_num_args</refname>
<refpurpose>
Returns the number of arguments passed to the function
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>func_num_args</function></funcdef>
<paramdef>void <parameter></parameter></paramdef>
</funcprototype>
</funcsynopsis>
<simpara>
Returns the number of arguments passed into the current
user-defined function. <function>Func_num_args</function> will
generate a warning if called from outside of a function
definition.
</simpara>
<para>
<informalexample>
<programlisting role="php">
&lt;?php
function foo() {
$numargs = func_num_args();
echo "Number of arguments: $numargs\n";
}
foo (1, 2, 3); // Prints 'Number of arguments: 3'
?&gt;
</programlisting>
</informalexample>
</para>
<simpara>
<function>Func_num_args</function> may be used in conjunction
with <function>func_get_arg</function> and
<function>func_get_args</function> to allow user-defined
functions to accept variable-length argument lists.
</simpara>
<note>
<simpara>
This function was added in PHP 4.
</simpara>
</note>
</refsect1>
</refentry>
<refentry id="function.function-exists">
<refnamediv>
<refname>function_exists</refname>
<refpurpose>
Return true if the given function has been defined
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>function_exists</function></funcdef>
<paramdef>string <parameter>function_name</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<simpara>
Checks the list of defined functions for
<parameter>function_name</parameter>. Returns true if the given
function name was found, false otherwise.
</simpara>
</refsect1>
</refentry>
<refentry id="function.register-shutdown-function">
<refnamediv>
<refname>register_shutdown_function</refname>
<refpurpose>
Register a function for execution on shutdown
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>int
<function>register_shutdown_function</function>
</funcdef>
<paramdef>string <parameter>func</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<simpara>
Registers the function named by <parameter>func</parameter> to be
executed when script processing is complete.</simpara>
<para>
Common Pitfalls:
</para>
<simpara>
Since no output is allowed to the browser in this function, you
will be unable to debug it using statements such as print or
echo.
</simpara>
</refsect1>
</refentry>
</reference>
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