| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|---|
| 2 | <html>
|
|---|
| 3 | <!-- Copyright (C) 2022 Richard Stallman and Free Software Foundation, Inc.
|
|---|
| 4 |
|
|---|
| 5 | (The work of Trevis Rothwell and Nelson Beebe has been assigned or
|
|---|
| 6 | licensed to the FSF.)
|
|---|
| 7 |
|
|---|
| 8 | Permission is granted to copy, distribute and/or modify this document
|
|---|
| 9 | under the terms of the GNU Free Documentation License, Version 1.3 or
|
|---|
| 10 | any later version published by the Free Software Foundation; with the
|
|---|
| 11 | Invariant Sections being "GNU General Public License," with the
|
|---|
| 12 | Front-Cover Texts being "A GNU Manual," and with the Back-Cover
|
|---|
| 13 | Texts as in (a) below. A copy of the license is included in the
|
|---|
| 14 | section entitled "GNU Free Documentation License."
|
|---|
| 15 |
|
|---|
| 16 | (a) The FSF's Back-Cover Text is: "You have the freedom to copy and
|
|---|
| 17 | modify this GNU manual. Buying copies from the FSF supports it in
|
|---|
| 18 | developing GNU and promoting software freedom." -->
|
|---|
| 19 | <!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|---|
| 20 | <head>
|
|---|
| 21 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|---|
| 22 | <title>The main Function (GNU C Language Manual)</title>
|
|---|
| 23 |
|
|---|
| 24 | <meta name="description" content="The main Function (GNU C Language Manual)">
|
|---|
| 25 | <meta name="keywords" content="The main Function (GNU C Language Manual)">
|
|---|
| 26 | <meta name="resource-type" content="document">
|
|---|
| 27 | <meta name="distribution" content="global">
|
|---|
| 28 | <meta name="Generator" content="makeinfo">
|
|---|
| 29 | <link href="index.html" rel="start" title="Top">
|
|---|
| 30 | <link href="Symbol-Index.html" rel="index" title="Symbol Index">
|
|---|
| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|---|
| 32 | <link href="Functions.html" rel="up" title="Functions">
|
|---|
| 33 | <link href="Values-from-main.html" rel="next" title="Values from main">
|
|---|
| 34 | <link href="Calling-Function-Pointers.html" rel="prev" title="Calling Function Pointers">
|
|---|
| 35 | <style type="text/css">
|
|---|
| 36 | <!--
|
|---|
| 37 | a.summary-letter {text-decoration: none}
|
|---|
| 38 | blockquote.indentedblock {margin-right: 0em}
|
|---|
| 39 | div.display {margin-left: 3.2em}
|
|---|
| 40 | div.example {margin-left: 3.2em}
|
|---|
| 41 | div.lisp {margin-left: 3.2em}
|
|---|
| 42 | kbd {font-style: oblique}
|
|---|
| 43 | pre.display {font-family: inherit}
|
|---|
| 44 | pre.format {font-family: inherit}
|
|---|
| 45 | pre.menu-comment {font-family: serif}
|
|---|
| 46 | pre.menu-preformatted {font-family: serif}
|
|---|
| 47 | span.nolinebreak {white-space: nowrap}
|
|---|
| 48 | span.roman {font-family: initial; font-weight: normal}
|
|---|
| 49 | span.sansserif {font-family: sans-serif; font-weight: normal}
|
|---|
| 50 | ul.no-bullet {list-style: none}
|
|---|
| 51 | -->
|
|---|
| 52 | </style>
|
|---|
| 53 |
|
|---|
| 54 |
|
|---|
| 55 | </head>
|
|---|
| 56 |
|
|---|
| 57 | <body lang="en">
|
|---|
| 58 | <span id="The-main-Function"></span><div class="header">
|
|---|
| 59 | <p>
|
|---|
| 60 | Next: <a href="Advanced-Definitions.html" accesskey="n" rel="next">Advanced Definitions</a>, Previous: <a href="Function-Pointers.html" accesskey="p" rel="prev">Function Pointers</a>, Up: <a href="Functions.html" accesskey="u" rel="up">Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
|
|---|
| 61 | </div>
|
|---|
| 62 | <hr>
|
|---|
| 63 | <span id="The-main-Function-1"></span><h3 class="section">22.6 The <code>main</code> Function</h3>
|
|---|
| 64 | <span id="index-main-function"></span>
|
|---|
| 65 | <span id="index-main"></span>
|
|---|
| 66 |
|
|---|
| 67 | <p>Every complete executable program requires at least one function,
|
|---|
| 68 | called <code>main</code>, which is where execution begins. You do not have
|
|---|
| 69 | to explicitly declare <code>main</code>, though GNU C permits you to do so.
|
|---|
| 70 | Conventionally, <code>main</code> should be defined to follow one of these
|
|---|
| 71 | calling conventions:
|
|---|
| 72 | </p>
|
|---|
| 73 | <div class="example">
|
|---|
| 74 | <pre class="example">int main (void) {<span class="roman">…</span>}
|
|---|
| 75 | int main (int argc, char *argv[]) {<span class="roman">…</span>}
|
|---|
| 76 | int main (int argc, char *argv[], char *envp[]) {<span class="roman">…</span>}
|
|---|
| 77 | </pre></div>
|
|---|
| 78 |
|
|---|
| 79 | <p>Using <code>void</code> as the parameter list means that <code>main</code> does
|
|---|
| 80 | not use the arguments. You can write <code>char **argv</code> instead of
|
|---|
| 81 | <code>char *argv[]</code>, and likewise for <code>envp</code>, as the two
|
|---|
| 82 | constructs are equivalent.
|
|---|
| 83 | </p>
|
|---|
| 84 |
|
|---|
| 85 | <p>You can call <code>main</code> from C code, as you can call any other
|
|---|
| 86 | function, though that is an unusual thing to do. When you do that,
|
|---|
| 87 | you must write the call to pass arguments that match the parameters in
|
|---|
| 88 | the definition of <code>main</code>.
|
|---|
| 89 | </p>
|
|---|
| 90 | <p>The <code>main</code> function is not actually the first code that runs when
|
|---|
| 91 | a program starts. In fact, the first code that runs is system code
|
|---|
| 92 | from the file <samp>crt0.o</samp>. In Unix, this was hand-written assembler
|
|---|
| 93 | code, but in GNU we replaced it with C code. Its job is to find
|
|---|
| 94 | the arguments for <code>main</code> and call that.
|
|---|
| 95 | </p>
|
|---|
| 96 | <table class="menu" border="0" cellspacing="0">
|
|---|
| 97 | <tr><td align="left" valign="top">• <a href="Values-from-main.html" accesskey="1">Values from main</a></td><td> </td><td align="left" valign="top">Returning values from the main function.
|
|---|
| 98 | </td></tr>
|
|---|
| 99 | <tr><td align="left" valign="top">• <a href="Command_002dline-Parameters.html" accesskey="2">Command-line Parameters</a></td><td> </td><td align="left" valign="top">Accessing command-line parameters
|
|---|
| 100 | provided to the program.
|
|---|
| 101 | </td></tr>
|
|---|
| 102 | <tr><td align="left" valign="top">• <a href="Environment-Variables.html" accesskey="3">Environment Variables</a></td><td> </td><td align="left" valign="top">Accessing system environment variables.
|
|---|
| 103 | </td></tr>
|
|---|
| 104 | </table>
|
|---|
| 105 |
|
|---|
| 106 | <hr>
|
|---|
| 107 | <div class="header">
|
|---|
| 108 | <p>
|
|---|
| 109 | Next: <a href="Advanced-Definitions.html" accesskey="n" rel="next">Advanced Definitions</a>, Previous: <a href="Function-Pointers.html" accesskey="p" rel="prev">Function Pointers</a>, Up: <a href="Functions.html" accesskey="u" rel="up">Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
|
|---|
| 110 | </div>
|
|---|
| 111 |
|
|---|
| 112 |
|
|---|
| 113 |
|
|---|
| 114 | </body>
|
|---|
| 115 | </html>
|
|---|
