Can a C program execute successfully if main() is defined as a macro?

We know that main() is the entry point of a C program. But what happens if we define main as a macro, like this?

#define main something_else

• Will the program compile and run correctly?
• How do different compilers handle this situation?
• Are there any cases where redefining main as a macro might be useful or problematic?

Barring any linker magic, your program would fail to link due to a missing main function.

For example if this was your full code:

#define main something_else

int main()
{
    return 0;
}

The output of the preprocessor would be this:

int something_else()
{
    return 0;
}

And you'd get a linker error:

/usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status