C++20 support in Visual Studio

Question

I'm wanting to use std::format but Visual Studio says the std namespace has no member format.

It appears this is new for C++20. Is there a way to make it available?

Answer 1

As of the time of writing, no C++ standard library implements std::format.

There are various implementations available on the web, like https://github.com/fmtlib/fmt (presumably the original source of the proposal, in fmt::) and https://github.com/mknejp/std-format (which puts everything in std::experimental::).

I wouldn't recommend pulling these into std. If I had to deal with something like this, the solution I would go for would be:

• Add a #define <some-unique-name>_format <wherever>::format and then use <some-unique-name>_format.

• Then, once you get std::format support, search-and-replace <some-unique-name>_format with std::format and toss the #define.

It uses macros, but in the long run it's better than having unqualified format everywhere.

Answer 2

You can use fmt as a sort of polyfill. It's not identical but has a significant feature overlap. So if you're careful about how you use it you can swap it out for <format> once support is there.

#include <string>
#include <version>
#ifndef __cpp_lib_format
#include <fmt/core.h>
using fmt::format;
#else
#include <format>
using std::format;
#endif

int main()
{
    std::string a = format("test {}",43);
    return 0;
}

Answer 3

As of the release of Visual Studio 2019 version 16.10 (released May 25th 2021) support was added for std::format. Just compile with /std:c++latest.