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<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright &copy; 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.   <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below).  A copy of the license isincluded in the section entitled "GNU Free Documentation License".   <p>(a) The FSF's Front-Cover Text is:   <p>A GNU Manual   <p>(b) The FSF's Back-Cover Text is:   <p>You have freedom to copy and modify this GNU Manual, like GNU     software.  Copies published by the Free Software Foundation raise     funds for GNU development.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!--  pre.display { font-family:inherit }  pre.format  { font-family:inherit }  pre.smalldisplay { font-family:inherit; font-size:smaller }  pre.smallformat  { font-family:inherit; font-size:smaller }  pre.smallexample { font-size:smaller }  pre.smalllisp    { font-size:smaller }--></style></head><body><div class="node"><p>Node:&nbsp;<a name="Constructing%20Calls">Constructing Calls</a>,Next:&nbsp;<a rel="next" accesskey="n" href="Typeof.html#Typeof">Typeof</a>,Previous:&nbsp;<a rel="previous" accesskey="p" href="Nested-Functions.html#Nested%20Functions">Nested Functions</a>,Up:&nbsp;<a rel="up" accesskey="u" href="C-Extensions.html#C%20Extensions">C Extensions</a><hr><br></div><h3 class="section">Constructing Function Calls</h3><p>Using the built-in functions described below, you can recordthe arguments a function received, and call another functionwith the same arguments, without knowing the number or typesof the arguments.   <p>You can also record the return value of that function call,and later return that value, without knowing what data typethe function tried to return (as long as your caller expectsthat data type).   <p>However, these built-in functions may interact badly with somesophisticated features or other extensions of the language.  Itis, therefore, not recommended to use them outside very simplefunctions acting as mere forwarders for their arguments.<p><table width="100%"><tr><td align="left">void * <b>__builtin_apply_args</b><i> </i>(<i></i>)<i>     </i></td><td align="right">Built-in Function</td></tr></table><table width="95%" align="center"><tr><td>This built-in function returns a pointer to datadescribing how to perform a call with the same arguments as were passedto the current function.     <p>The function saves the arg pointer register, structure value address,and all registers that might be used to pass arguments to a functioninto a block of memory allocated on the stack.  Then it returns theaddress of that block. </td></tr></table><p><table width="100%"><tr><td align="left">void * <b>__builtin_apply</b><i> </i>(<i>void </i>(<i>*</i><var>function</var><i></i>)<i></i>(<i></i>)<i>, void *</i><var>arguments</var><i>, size_t </i><var>size</var><i></i>)<i>     </i></td><td align="right">Built-in Function</td></tr></table><table width="95%" align="center"><tr><td>This built-in function invokes <var>function</var>with a copy of the parameters described by <var>arguments</var>and <var>size</var>.     <p>The value of <var>arguments</var> should be the value returned by<code>__builtin_apply_args</code>.  The argument <var>size</var> specifies the sizeof the stack argument data, in bytes.     <p>This function returns a pointer to data describinghow to return whatever value was returned by <var>function</var>.  The datais saved in a block of memory allocated on the stack.     <p>It is not always simple to compute the proper value for <var>size</var>.  Thevalue is used by <code>__builtin_apply</code> to compute the amount of datathat should be pushed on the stack and copied from the incoming argumentarea. </td></tr></table><p><table width="100%"><tr><td align="left">void <b>__builtin_return</b><i> </i>(<i>void *</i><var>result</var><i></i>)<i>     </i></td><td align="right">Built-in Function</td></tr></table><table width="95%" align="center"><tr><td>This built-in function returns the value described by <var>result</var> fromthe containing function.  You should specify, for <var>result</var>, a valuereturned by <code>__builtin_apply</code>. </td></tr></table>   </body></html>
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