在 Visual Studio 中编译时出现编译错误 C2048，但在 clang++ 中可以正常工作吗？

Question

I tried to compile the following sample code with clang compiler and it works fine.

• Compiler Details: Apple clang version 12.0.0 (clang-1200.0.32.28)
• Target: x86_64-apple-darwin20.1.0

#include <iostream>
#include <stdio.h>

int __cdecl printf(const char* format, ...)
{
    std::cout<<"My printf function"<<std::endl;
    return 0;
}

int main()
{
    printf("Standard printf function\n");
    return 0;
}

However, when I tried to compile in visual studio 2019 or g++, it gives compilation error.

error C2084: function 'int printf(const char *const,...)' already has a body

• What is the reason of compilation failure with msvc?
• How can I make it work, what am I missing?

Answer 1

From your code you are intentionally trying to use your own version of the printf function.

The error C2084 is expected. You are redefining something already defined. It's dangerous, and you be aware of the risks you are taking. It's a piece of a whole library and any UB (undefined Behaviour) may arise. I won't play with that. From my perspective it's g++ that is not reporting an error, but it may be that the g++/libc prototype of printf is slightly different from the one you wrote, or even, the function printf is declared in the header but not defined in there.

If you really want go down that way I strongly suggest you to define your printf in another source file and hide the libc implementation at linking time. That should be allowed (Warning and errors may arise, but every linker has an override for that).