Function with auto parameter compiles using GCC but does not compile using Visual C++

问题

Please considere the following code-snippet:

#include <iostream> 

void print(auto arg) {
  std::cout << arg << std::endl;
}

int main() {
  print("Hi");

  return 0;
}

As you can see here (https://godbolt.org/z/2GSrXs) using GCC the code compiles and runs fine.

As you can see here (https://godbolt.org/z/rtR6w9) using Visual C++ the code does not compile and results in the error message:

<source>(3): error C3533: a parameter cannot have a type that contains 'auto'.

It seems to me that this feature has not jet been implementet in Visual C++? Additionally I was not able to find the compiler feature in the following list: https://docs.microsoft.com/en-us/cpp/overview/visual-cpp-language-conformance?view=vs-2019. So I am not sure if the Microsoft developer have the feature on their ToDo List?

回答1:

Functions receiving auto is a C++20 feature. It must be enabled with /std:latest. However, MSVC only has partial support for this syntax at this time, so not all declaration using this feature will work.

GCC has supported auto in function parameters since early C++14 days as an extension.

You can read more about this C++20 feature reading P1141R2: Yet another approach for constrained declarations

回答2:

Remaining in C++14 standard, you can use the following lambda instead of your function:

auto print = [](auto arg) {
    std::cout << arg << std::endl;
};

来源：https://stackoverflow.com/questions/62516242/function-with-auto-parameter-compiles-using-gcc-but-does-not-compile-using-visua