如何从 mingw、c++（或 c）获取和设置环境变量

Question

I am writing a program that needs to set environment variables for the current process from mingw (to be available for subprocesses when using system(...) -call).

I know how to do in linux, and windows with msvc and clang. However, I cannot find any goood examples on how to do it with mingw-g++ .

How do I implement functions that has this kind of behaviour?

// Example usage:
void setVar(std::string name, std::string value) {
    // How to do this
}

std::string getVar(std::string name) {
    // ... and this
}

If you want to answer in c, feel free to omit std::string:)

Edit:

When using setenv (the linux way) i get:

src/env.cpp: In function 'void appendEnv(std::string, std::string)':
src/env.cpp:46:5: error: 'setenv' was not declared in this scope; did you mean 'getenv'?
   46 |     setenv(name.c_str(), value.c_str(), 1);
      |     ^~~~~~
      |     getenv

When using _putenv_s (the way i have used for msvc and clang on windows) I get.

src/env.cpp: In function 'int setenv(const char*, const char*, int)':
src/env.cpp:16:12: error: '_putenv_s' was not declared in this scope; did you mean '_putenv_r'?
   16 |     return _putenv_s(name, value);
      |            ^~~~~~~~~
      |            _putenv_r

Answer 1

With inspirations from the comments i found this question on putenv

and managed to whip together this prototype application:

#include <cstdlib> // For system(...)

#ifdef __MINGW32__
extern int putenv(char *); // Not defined by mingw
#endif

int main() {
    putenv(const_cast<char *>("x=10"));
    system("set"); // Output variables to se if it works

    return 0;
}

Resulting output:

....
x=10

Thanks for the help!