Passing class member functions as a parameter to a non-class function.

[Wynner]

I'm an old Delphi programmer getting into the C++ world, and trying to wrap my head around this problem.

I have multiple classes derived from a generic class that passes one of it's functions as a parameter to another function. The code is very complex, so I've written this abridged version of what I am trying to do.

// genClass.h
#ifndef genClassH
#define genClassH
 
#include <Classes.hpp>
 
// Class declerations
class genClass
{
  virtual char *doStuff(char *) = 0;
  char *doIt(char *,char *);
};
 
class getFive : genClass
{
  char *doStuff(char *input);
};
 
class getThree : genClass
{
  char *doStuff(char *input);
};
 
// Function
char *genFunc(char *,char *(*func)(char *));
 
#endif

// genClass.cpp
#pragma hdrstop
#include "genClass.h"
#pragma package(smart_init)
 
// Class member definitions
char *getFive::doStuff(char *input)
{
  char *result;
  strncpy(result,input,5);
  return result;
}
 
char *getThree::doStuff(char *input)
{
  char *result;
  strncpy(result,input,3);
  return result;
}
 
char *genClass::doIt(char *pre,char *str)
{
  return genFunc(pre,doStuff(str));
}
 
// Function definition
char *genFunc(char *pre,char *(*func)(char *input))
{
  char *result;
  strcpy(result,pre);
  strcat(result,func);
  return result;
}

I'm trying to compile this in Borland C++ Builder. I think I've overly confused myself, but this is where I'm stuck.

My error message is:
[C++ Error] genClass.cpp(23 ): E2034 Cannot convert 'char *' to 'char * (*)(char *)'

TIA for any help.

[weaknessforcats]

Several things:

1)There are no public/private specifiers. You will probably need these.

2) This code:

char *getFive::doStu ff(char *input)
{
char *result;
strncpy(result, input,5);
return result;
}

does not allocate memory for result before copying data to that location. Guranteed program crash here. Other places have the same problem.

3) This code:

char *genClass::doIt (char *pre,char *str)
{
return genFunc(pre,doS tuff(str));
}

does a call to doStuff(str). That call returns a char*. The argument is supposed to be a function pointer. Hence, the compiler bark about not being able to convert a char* to a function pointer.

4) What are you trying to do??
The way these classes are set up and used looks very incorrect.