What is pragma in C? Or how will you execute functions before and after main function in C program?

In C, #pragma is a preprocessor directive that provides additional information to the compiler. It is a way to give special instructions to the compiler about how to process the code. The #pragma directive is followed by an identifier that indicates the specific action to be taken.

Regarding executing functions before and after the main function in a C program, you can use the #pragma startup and #pragma exit directives.

1. Before main Function:

<span class="pln">
</span><span class="com">#include</span><span class="pln"> </span><span class="str">&lt;stdio.h&gt;</span><span class="pln">

</span><span class="kwd">void</span><span class="pln"> startup_function</span><span class="pun">(</span><span class="kwd">void</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    printf</span><span class="pun">(</span><span class="str">"Function executed before main\n"</span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span><span class="pln">

</span><span class="com">#pragma</span><span class="pln"> startup startup_function

</span><span class="kwd">int</span><span class="pln"> main</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    printf</span><span class="pun">(</span><span class="str">"Inside main function\n"</span><span class="pun">);</span><span class="pln">
    </span><span class="kwd">return</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span>

1. The #pragma startup directive is used to specify a function (startup_function in this case) that will be executed before the main function.

2. After main Function:

<span class="pln">
</span><span class="com">#include</span><span class="pln"> </span><span class="str">&lt;stdio.h&gt;</span><span class="pln">

</span><span class="kwd">void</span><span class="pln"> exit_function</span><span class="pun">(</span><span class="kwd">void</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    printf</span><span class="pun">(</span><span class="str">"Function executed after main\n"</span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span><span class="pln">

</span><span class="com">#pragma</span><span class="pln"> </span><span class="kwd">exit</span><span class="pln"> exit_function

</span><span class="kwd">int</span><span class="pln"> main</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    printf</span><span class="pun">(</span><span class="str">"Inside main function\n"</span><span class="pun">);</span><span class="pln">
    </span><span class="kwd">return</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span>

1. The #pragma exit directive is used to specify a function (exit_function in this case) that will be executed after the main function.

It's important to note that the usage of #pragma directives is compiler-specific, and not all compilers support these directives. The examples provided here are based on compilers that support these specific directives, like Turbo C or certain versions of GCC. Always check the documentation of your compiler for the supported directives and their behavior.