Why a warning of “control reaches end of non-void function” for the main function?

Question

I run the following C codes and got a warning: control reaches end of non-void function

int main(void) {}

Any suggestions?

Answer 1

As an alternative to the obvious solution of adding a return statement to main(), you can use a C99 compiler (“gcc -std=c99” if you are using GCC).

In C99 it is legal for main() not to have a return statement, and then the final } implicitly returns 0.

$ gcc -c -Wall t.c
t.c: In function ‘main’:
t.c:20: warning: control reaches end of non-void function
$ gcc -c -Wall -std=c99 t.c
$ 

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A note that purists would consider important: you should not fix the warning by declaring main() as returning type void.