[SOLVED] Why does gcc warn about decltype(main()) but not clang?

Issue

Take the following code:

int main()
{
    decltype(main()) x = 0;
    return x;
}

gcc complains:

main.cpp: In function 'int main()':
main.cpp:8:19: warning: ISO C++ forbids taking address of function '::main' [-Wpedantic]
     decltype(main()) x = 0;
                   ^
main.cpp:8:19: warning: ISO C++ forbids taking address of function '::main' [-Wpedantic]

but not clang. So what about decltype(main()) raises this error? How does decltype take the address of main?

Solution

GCC's diagnostic might not be correctly phrased in this case, because decltype doesn't need to know the address of main; it only needs to know its type. However, the warning is based on the following from the standard (§3.6.1/3):

The function main shall not be used within a program.

I suppose GCC interprets this to mean that you can't even use it in an unevaluated expression.

Clang (version 3.4 anyway) appears to not implement this rule at all, even if I turn on all the flags I can think of and even if main calls itself recursively. That's why it doesn't give you a warning.

Answered By - Brian Bi

Answer Checked By - Timothy Miller (WPSolving Admin)