How to Call C++ Class from C

Calling a C++ class from C can be a bit tricky because C does not support classes and objects like C++. However, you can still interact with C++ code from C by creating a C interface for your C++ class. In this example, we define a C++ class MyClass with a method doSomething(). Then, we create a C wrapper MyClassWrapper that provides functions to create, manipulate, and destroy instances of MyClass. Finally, we can use these functions in a C program to interact with the MyClass object. See github.

Define a C++ class

#ifndef MYCLASS_H
#define MYCLASS_H

class MyClass {
public:
    MyClass();
    void doSomething();
private:
    int data;
};
#endif // MYCLASS_H

#include "MyClass.h"
#include <iostream>

MyClass::MyClass() : data(0) {}

void MyClass::doSomething() {
    std::cout << "Doing something in MyClass" << std::endl;
}

Define a C wrapper

// MyClassWrapper.h
#ifndef MYCLASSWRAPPER_H
#define MYCLASSWRAPPER_H

#ifdef __cplusplus
extern "C" {
#endif

typedef void* MyClassHandle;

MyClassHandle createMyClass();
void destroyMyClass(MyClassHandle obj);
void doSomethingInMyClass(MyClassHandle obj);

#ifdef __cplusplus
}
#endif

#endif // MYCLASSWRAPPER_H

#include "MyClassWrapper.h"
#include "MyClass.h"

extern "C" {

MyClassHandle createMyClass() {
    return reinterpret_cast<MyClassHandle>(new MyClass());
}

void destroyMyClass(MyClassHandle obj) {
    delete reinterpret_cast<MyClass*>(obj);
}

void doSomethingInMyClass(MyClassHandle obj) {
    reinterpret_cast<MyClass*>(obj)->doSomething();
}
}

Use the wrapper in C

#include "MyClassWrapper.h"

int main() {
    MyClassHandle obj = createMyClass();
    doSomethingInMyClass(obj);
    destroyMyClass(obj);
    return 0;
}