php-doc-en/internals/zendapi/calling-user-functions.xml

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 <sect1 id="zend.calling-user-functions"> 
  <title>Calling User Functions</title> 
  <para>
   You can call user functions from your own modules, which is very
   handy when implementing callbacks; for example, for array walking, searching, or
   simply for event-based programs.
  </para> 
  <para>
   User functions can be called with the
   function <function>call_user_function_ex</function>. It requires a hash value
   for the function table you want to access, a pointer to an object (if you want
   to call a method), the function name, return value, number of arguments,
   argument array, and a flag indicating whether you want to perform zval separation. 
  </para>
  <programlisting>
ZEND_API int call_user_function_ex(HashTable *function_table, zval *object,
zval *function_name, zval **retval_ptr_ptr,
int param_count, zval **params[],
int no_separation);
  </programlisting>
  <para>
   Note that you don't have to specify both
   <envar>function_table</envar>  and <envar>object</envar>; either
   will do. If you want to call a method, you have to supply the
   object that contains this method, in which case
   <function>call_user_function</function>automatically sets the
   function table to this object's function table. Otherwise, you only
   need to specify <envar>function_table</envar> and can set
   <envar>object</envar> to <literal>NULL</literal>.
  </para> 
  <para>
   Usually, the default function table is the "root" function table
   containing all function entries. This function table is part of the
   compiler globals and can be accessed using the macro
   <literal>CG</literal>. To introduce the compiler globals to your
   function, call the macro <literal>TSRMLS_FETCH</literal> once.
  </para>
  <para>
   The function name is specified in a <envar>zval</envar>
   container. This might be a bit surprising at first, but is quite a
   logical step, since most of the time you'll accept function names
   as parameters from calling functions within your script, which in
   turn are contained in <envar>zval</envar> containers again. Thus,
   you only have to pass your arguments through to this function. This
   <envar>zval</envar> must be of type <literal>IS_STRING</literal>.
  </para>
  <para>
   The next argument consists of a pointer to the return value. You
   don't have to allocate memory for this container; the function will
   do so by itself. However, you have to destroy this container (using
   <function>zval_dtor</function>) afterward!
  </para> 
  <para>
   Next is the parameter count as integer and an array containing all
   necessary parameters.  The last argument specifies whether the
   function should perform zval separation - this should always be set
   to <literal>0</literal>. If set to <literal>1</literal>, the
   function consumes less memory but fails if any of the parameters
   need separation.
  </para> 
  <para>
   <xref linkend='example.call-user-func'/> shows a small demonstration of
   calling a user function. The code calls a function that's supplied
   to it as argument and directly passes this function's return value
   through as its own return value. Note the use of the constructor
   and destructor calls at the end - it might not be necessary to do
   it this way here (since they should be separate values, the
   assignment might be safe), but this is bulletproof.
  </para> 
  <example id='example.call-user-func'> 
   <title>Calling user functions.</title> 
   <programlisting>
zval **function_name;
zval *retval;

if((ZEND_NUM_ARGS() != 1) || (zend_get_parameters_ex(1, &amp;function_name) != SUCCESS))
{
    WRONG_PARAM_COUNT;
}

if((*function_name)-&gt;type != IS_STRING)
{
    zend_error(E_ERROR, "Function requires string argument");
}

TSRMSLS_FETCH();

if(call_user_function_ex(CG(function_table), NULL, *function_name, &amp;retval, 0, NULL, 0) != SUCCESS)
{
    zend_error(E_ERROR, "Function call failed");
}

zend_printf("We have %i as type&lt;br&gt;", retval-&gt;type);

*return_value = *retval;
zval_copy_ctor(return_value);
zval_ptr_dtor(&amp;retval);
   </programlisting> 
  </example> 
  <para/>
   <programlisting>
&lt;?php

dl("call_userland.so");

function test_function()
{

    print("We are in the test function!&lt;br&gt;");

    return("hello");

}

$return_value = call_userland("test_function");

print("Return value: \"$return_value\"&lt;br&gt;");
?&gt;
   </programlisting>
   <graphic fileref="figures/zend.10-userland.png"/> 
 </sect1> 
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