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<p>A program shall contain a global function named <code><b>main</b></code>, which is the designated start of the program.
</p>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> <code><b>main</b></code> <code><b>()</b></code> <code><b>{</b></code> <span class="t-spar">body</span> <code><b>} </b></code>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> <code><b>main</b></code> <code><b>(</b></code><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> <span class="t-spar">argc</span><code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span></span></span><span class="t-spar">argv</span><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">]</span></span></span><code><b>)</b></code> <code><b>{</b></code> <span class="t-spar">body</span> <code><b>} </b></code>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> <code><b>main</b></code> <code><b>(</b></code><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> <span class="t-spar">argc</span><code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span></span></span><span class="t-spar">argv</span><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">]</span></span></span> <code><b>,</b></code> <span class="t-spar">other_parameters</span> <code><b>)</b></code> <code><b>{</b></code> <span class="t-spar">body</span> <code><b>} </b></code>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<table class="t-par-begin">
<tr class="t-par">
<td> argc
</td>
<td> -
</td>
<td> Non-negative value representing the number of arguments passed to the program from the environment in which the program is run.
</td></tr>
<tr class="t-par">
<td> argv
</td>
<td> -
</td>
<td> Pointer to the first element of an array of pointers to <a href="../string/multibyte.html" title="cpp/string/multibyte">null-terminated multibyte strings</a> that represent the arguments passed to the program from the execution environment (<span class="t-c"><span class="mw-geshi cpp source-cpp">argv<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span></span></span> through <span class="t-c"><span class="mw-geshi cpp source-cpp">argv<span class="br0">[</span>argc<span class="sy2">-</span><span class="nu0">1</span><span class="br0">]</span></span></span>). The value of <span class="t-c"><span class="mw-geshi cpp source-cpp">argv<span class="br0">[</span>argc<span class="br0">]</span></span></span> is guaranteed to be <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">0</span></span></span>.
</td></tr>
<tr class="t-par">
<td> body
</td>
<td> -
</td>
<td> The body of the main function
</td></tr>
<tr class="t-par">
<td> <span class="t-spar">other_parameters</span>
</td>
<td> -
</td>
<td> Implementations may allow additional forms of the main function as long as the return type remains <code>int</code>. A very common extension is passing a third argument of type <code>char*[]</code> pointing at <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html">an array of pointers to the execution environment variables</a>.
</td></tr></table>
<p>The names <code>argc</code> and <code>argv</code> are arbitrary, as well as the representation of the types of the parameters: <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">int</span> ac, <span class="kw4">char</span><span class="sy2">**</span> av<span class="br0">)</span></span></span> is equally valid.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/main_function&action=edit&section=1" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span></h3>
<p>The <code>main</code> function is called at program startup after <a href="initialization.html" title="cpp/language/initialization">initialization</a> of the non-local objects with static <a href="storage_duration.html" title="cpp/language/storage duration">storage duration</a>. It is the designated entry point to a program that is executed in <i>hosted</i> environment (that is, with an operating system). The entry points to <i>freestanding</i> programs (boot loaders, OS kernels, etc) are implementation-defined.
</p><p>The parameters of the two-parameter form of the main function allow arbitrary multibyte character strings to be passed from the execution environment (these are typically known as <i>command line arguments</i>), the pointers <code>argv[1] .. argv[argc-1]</code> point at the first characters in each of these strings. <code>argv[0]</code> is the pointer to the initial character of a null-terminated multibyte strings that represents the name used to invoke the program itself (or an empty string <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">""</span></span></span> if this is not supported by the execution environment). The strings are modifiable, although these modifications do not propagate back to the execution environment: they can be used, for example, with <span class="t-lc"><a href="../string/byte/strtok.html" title="cpp/string/byte/strtok">std::strtok</a></span>. The size of the array pointed to by <code>argv</code> is at least <code>argc+1</code>, and the last element, <code>argv[argc]</code>, is guaranteed to be a null pointer.
</p><p>The <code>main</code> function has several special properties:
</p>
<div class="t-li1"><span class="t-li">1)</span> It cannot be used anywhere in the program</div>
<div class="t-li2"><span class="t-li">a)</span> in particular, it cannot be called recursively</div>
<div class="t-li2"><span class="t-li">b)</span> its address cannot be taken</div>
<div class="t-li1"><span class="t-li">2)</span> It cannot be predefined and cannot be overloaded: effectively, the name <code>main</code> in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace<span class="t-rev-inl t-since-cxx17"><span>, except that a function called "main" cannot be declared with C <a href="language_linkage.html" title="cpp/language/language linkage">language linkage</a> in any namespace</span> <span><span class="t-mark-rev t-since-cxx17">(since C++17)</span></span></span>)</div>
<div class="t-li1"><span class="t-li">3)</span> It cannot be defined as deleted or declared <span class="t-rev-inl t-since-cxx17"><span>with C <a href="language_linkage.html" title="cpp/language/language linkage">language linkage</a></span> <span><span class="t-mark-rev t-since-cxx17">(since C++17)</span></span></span>, <a href="inline.html" title="cpp/language/inline">inline</a>, <a href="static.html" title="cpp/language/static">static</a>, or <a href="constexpr.html" title="cpp/language/constexpr">constexpr</a></div>
<div class="t-li1"><span class="t-li">4)</span> The body of the main function does not need to contain the <a href="return.html" title="cpp/language/return">return statement</a>: if control reaches the end of <code>main</code> without encountering a return statement, the effect is that of executing <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span></span></span>.</div>
<div class="t-li1"><span class="t-li">5)</span> Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../utility/program/exit.html"><span class="kw812">std::<span class="me2">exit</span></span></a></span></span> with the same argument as the argument of the <a href="return.html" title="cpp/language/return">return</a>. (<span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../utility/program/exit.html"><span class="kw812">std::<span class="me2">exit</span></span></a></span></span> then destroys static objects and terminates the program)</div>
<div class="t-li1"><span class="t-li">6)</span> If the main function is defined with a <a href="function-try-block.html" title="cpp/language/function-try-block">function-try-block</a>, the exceptions thrown by the destructors of static objects (which are destroyed by the implied <span class="t-lc"><a href="../utility/program/exit.html" title="cpp/utility/program/exit">std::exit</a></span>) are not caught by it.</div>
<div class="t-li1"><span class="t-li">7)</span> <span class="t-mark-rev t-since-cxx14">(since C++14)</span> The return type of the main function cannot be deduced (<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">auto</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>...</span></span> is not allowed)</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/main_function&action=edit&section=2" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../../c/language/main_function.html" title="c/language/main function">C documentation</a></span> for <span class="t-dsc-see-tt"><span>main function</span></span></div>
</td></tr>
</table>
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