Can C 's `main()` Function Be Recursive?

Recursivity Restrictions in C 's main() Function

In C , the use of recursion within the main() function has been a subject of debate. Numerous developers have observed that the GNU Compiler Collection (g ) permits recursion in main() despite the alleged prohibition in the C standard.

Standard Restrictions

As per the C standard (3.6.1/3), recursion in main() is explicitly forbidden:

"The function main shall not be used (3.2) within a program."

Definition of "Used"

The standard also defines "used" as an object or non-overloaded function:

"An object or non-overloaded function is used if its name appears in a potentially-evaluated expression."

Therefore, calling main() from within itself constitutes "use" and is hence disallowed according to the standard.

Compiler Behavior

Despite the standard's prohibition, g compiles the following code without error:

int main()
{
    main();
}

This discrepancy arises because g 's default optimization level includes inlining functions smaller than a preconfigured threshold. Since the recursion in this code is a single function call, it likely falls below the threshold and is inlined by g .

Conclusion

While g may permit recursion in main() in some cases, the C standard strictly forbids it. Developers should adhere to the standard's requirements to ensure program correctness and potential pitfalls.

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