How do I interoperate with C APIs std::variant in C++?

Interoperating with C APIs using std::variant in C++ can enhance type safety and flexibility in handling different return types from C functions. Below is an example demonstrating how to create a simple C API that returns different types using std::variant. This allows for more robust error handling and streamlined data processing.

To start, we can define a C function that returns different types, and then in our C++ code, we will utilize std::variant to handle these return types.


    // C API Example
    #include 
    #include 

    typedef struct {
        enum { INT_TYPE, FLOAT_TYPE, STRING_TYPE } type;
        union {
            int i;
            float f;
            char *s;
        } value;
    } Variant;

    Variant get_variant(int choice) {
        Variant v;
        if (choice == 1) {
            v.type = INT_TYPE;
            v.value.i = 42;
        } else if (choice == 2) {
            v.type = FLOAT_TYPE;
            v.value.f = 3.14f;
        } else {
            v.type = STRING_TYPE;
            v.value.s = "Hello, World!";
        }
        return v;
    }

    // C++ code using std::variant
    #include 
    #include 
    #include 

    using MyVariant = std::variant;

    MyVariant getCVariant(int choice) {
        Variant v = get_variant(choice);
        switch(v.type) {
            case INT_TYPE: return v.value.i;
            case FLOAT_TYPE: return v.value.f;
            case STRING_TYPE: return std::string(v.value.s);
        }
        // Fallback in case of an invalid choice
        return 0; // or throw an exception
    }

    int main() {
        MyVariant var = getCVariant(2);
        std::visit([](auto&& arg){ std::cout << arg << '\n'; }, var);
        return 0;
    }

How do I interoperate with C APIs std::variant in C++?

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How do I interoperate with C APIs std::variant in C++?

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