Crash when building with `/MT` in MSVC (double-destructor)

[ZeroKwok]

Description

When building CPR with /MT (static CRT) on MSVC, CPR defines an inline const std::unordered_map as a global variable(include/cpr/error.h:93). With MSVC, each translation unit generates its own copy of the destructor registration code. Although the data are COMDAT-folded into a single instance, the destructor registrations are not folded, causing the same object to be registered multiple times for destruction.

As a result, CPR triggers multiple destructor calls on the same global object during program shutdown, which leads to double free / memory corruption / crash.

This issue does not appear with /MD, because the dynamic CRT deduplicates destructor registration internally.

Example/How to Reproduce

1. Build CPR using MSVC with /MT or /MTd
2. Include CPR headers in multiple translation units (may require calling 'to_string(code)')
3. Link and run the program
4. Program crashes on exit due to double-destruction of the inline global map

Possible Fix

Avoid inline global objects with non-trivial destructors.

// include/cpr/error.h:93
inline const std::unordered_map<ErrorCode, std::string> error_code_to_string_mapping = { /*...*/ };

Use a function-local static instead:

const std::unordered_map<...>& get_error_map() {
    static const std::unordered_map<...> map = {
        /* ... */
    };
    return map;
}

inline std::string to_string(const cpr::ErrorCode& code) {
    return cpr::error_code_map().at(code);
}

Or

inline std::string to_string(const cpr::ErrorCode& code) {
    static const std::unordered_map<...> error_code_to_string_mapping = { ... };
    return error_code_to_string_mapping.at(code);
}

Where did you get it from?

vcpkg

Additional Context/Your Environment

• OS: Windows 10/Windows 7
• Version: 1.12.0

[COM8]

Confirmed!
This might be the cause for this as well.
Would you like to create a PR for it? I prefer the pure get_error_map approach since the error map was previously public and people might rely on it.