调用std::to_chars处理double编译失败，如何正确调用？

Ah, I’ve run into this exact headache before! The root of the problem is incomplete C++17 standard support for floating-point std::to_chars in older GCC and Clang versions. Let’s break this down and get your code working.

Why This Happens #

The C++17 standard added std::to_chars overloads for floating-point types like double, but compiler implementations lagged:

• GCC didn’t fully implement these floating-point overloads until version 11. Version 10.2 has a partial, non-conforming implementation that causes overload resolution ambiguity.
• Clang didn’t add proper support for floating-point std::to_chars until around version 14. Version 10.0.1 simply lacks these overloads entirely, hence the "no matching function" error.

MSVC, by contrast, rolled out full support for these overloads much earlier, which is why your code works there without issues.

Solutions #

1. Upgrade Your Compiler (Recommended) #

If you can update your toolchain, this is the cleanest fix:

• For GCC: Upgrade to version 11 or newer.
• For Clang: Upgrade to version 14 or newer.

Once upgraded, your original code will run exactly as written—no changes required.

2. Fallback Implementation (If You Can’t Upgrade) #

If upgrading isn’t an option, use std::snprintf as a reliable, compiler-agnostic alternative. It’s fully compatible with C++17 and all older compilers:

#include <cstdio>
#include <string>

int main() {
    std::string str;
    str.resize(30);
    // Write the double to the string buffer
    int bytes_written = std::snprintf(str.data(), str.size(), "%.15g", 3.5);
    // Resize the string to match the actual characters written
    if (bytes_written > 0 && bytes_written < static_cast<int>(str.size())) {
        str.resize(bytes_written);
    }
}

The %.15g format specifier gives you a compact, accurate representation of the double (aligned with what std::to_chars aims for). Adjust the precision (e.g., %.20g) if you need more digits.

Another option is Boost’s lexical_cast, but that requires linking against the Boost library, which might not be ideal for minimal codebases.

Correct Call Syntax (For Supported Compilers) #

Just to confirm, once your compiler supports floating-point std::to_chars, your original code is perfectly valid. You can also explicitly clarify the overload if you want (though it’s rarely necessary):

auto[ptr, ec] = std::to_chars(str.data(), str.data() + str.size(), 3.5);
// Explicit cast to double (redundant here, but useful for edge cases)
auto[ptr, ec] = std::to_chars(str.data(), str.data() + str.size(), static_cast<double>(3.5));

内容的提问来源于stack exchange，提问作者lionkor