Question

I have an opensource lib in .c, it has 2 parameters, but they are hardcoded in .h file with #define. They are around all code.
Change the parameter-> recompile.
How can I do best design of my cpp wrapper to this to which I can pass some parameter values and will have ability to call code without recompiling it?

Answer 1

You can make them static members of a class and initialize them in an implementation file.

//header.h
class Hardcoded
{
public:
   static int param;
};

//implementation.cpp
#include "header.h"
int Hardcoded::param = 0;

or you could declare a free variable with extern which you initialize in an implementation file.

EDIT:

You can continue using macros if you don’t want to change the whole code, without requiring compilation every time you want to change the value:

#define PARAM Hardcoded::param

EDIT:

I now see what you mean:

#if QLZ_COMPRESSION_LEVEL == 1
        state->hash[i].offset = 0;
#else
        state->hash_counter[i] = 0;
#endif

In this case, it’s impossible to do what you want, and you shouldn’t do it anyway, because you need to compile a different thing every time the define changes. So it’s not a matter of re-compiling, it’s a matter that you need to recompile.