Question

I will have two files. One header.h file and second one is main.c file.

Now, how to make a header.h file with methods written in C (such as print test etc), then in main.c file, how can I access them with operators such as :: or ->

@file: main.c

#include "header.h"; // sorry i made mistake before

int main()
    {
      A::myStaticFunction();

      // OR

      A->myInstanceFunction();

      return 0;
    }

Answer 1

I would like to do it completely in C.
^{(from @Sonia’s comment on @Als’ answer)}

Not completely possible. What you got there is C++ code, it can’t be emulated in C in exactly that way.

In C, a struct can’t have functions, only function pointer and also can’t have any static members at all. So, no :: for you in that regard. Your other example, on @David’s answer, is most likely an enum:

typedef enum _H323Connection{
  AnswerCallNow,
  AnswerCallLater,
  IgnoreCall,
  /* examples */
}H323Connection;

Now, to get one of those values inside the enum you can just use the name (IgnoreCall) or qualify it with the enum’s name (H323Connection::IgnoreCall).

The -> operator, however, is totally possible.

typedef struct _sA{
  // function pointer
  void (*AnswerCall)(struct _sA*, H323Connection);
  // variables...
}sA;

void sA_AnswerCall(sA* self, H323Connection callmode){
  // do something with self
  switch(callmode){
    case AnswerCallNow: /* ... */ break;
    case AnswerCallLater: /* ... */ break;
    case IgnoreCall: /* ... */ break;
  }
}

int main(){
  sA* pA = (sA*)malloc(sizeof(sA));

  // assign function pointer;
  pA->AnswerCall = sA_AnswerCall;
  // call it and pass "this" (the object the function operates on)
  pA->AnswerCall(pA, H323Connection::AnswerCallNow);
  // in C++ ---- ^^ would be the "this" pointer and 
  // would be passed secretly by the compiler

  free(pA);
}