How to call C++ function from C?

You need to create a C API for exposing the functionality of your C++ code. Basically, you will need to write C++ code that is declared extern “C” and that has a pure C API (not using classes, for example) that wraps the C++ library. Then you use the pure C wrapper library that you’ve created.

Your C API can optionally follow an object-oriented style, even though C is not object-oriented. Ex:

// *.h file
// ...
#ifdef __cplusplus
#define EXTERNC extern "C"
#else
#define EXTERNC
#endif

typedef void* mylibrary_mytype_t;

EXTERNC mylibrary_mytype_t mylibrary_mytype_init();
EXTERNC void mylibrary_mytype_destroy(mylibrary_mytype_t mytype);
EXTERNC void mylibrary_mytype_doit(mylibrary_mytype_t self, int param);

#undef EXTERNC
// ...

// *.cpp file
mylibrary_mytype_t mylibrary_mytype_init() {
  return new MyType;
}

void mylibrary_mytype_destroy(mylibrary_mytype_t untyped_ptr) {
   MyType* typed_ptr = static_cast<MyType*>(untyped_ptr);
   delete typed_ptr;
}

void mylibrary_mytype_doit(mylibrary_mytype_t untyped_self, int param) {
   MyType* typed_self = static_cast<MyType*>(untyped_self);
   typed_self->doIt(param);
}