String.c

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include "String.h"

static void assign_s(String *this, const String *str);
static void assign_c(String *this, const char *s);
static void append_s(String *this, const String *ap);
static void append_c(String *this, const char *ap);

void    StringInit(String *this, const char *s)
{
  if (this)
    this->str = strdup(s);
  this->assign_s = &assign_s;
  this->assign_c = &assign_c;
}

void    StringDestroy(String *this)
{
  if (!this)
    return;
  if (this->str)
    free(this->str);
  free(this);
}

static void     safe_free(void *data)
{
  void          **addr = (void **) data;

  if (addr && *addr)
    free(*addr);
  *addr = NULL;
}

static void assign_s(String *this, const String *str)
{
  if (!this || !str)
    return;
  safe_free(&this->str);
  if (str->str)
    this->str = strdup(str->str);
}

static void assign_c(String *this, const char *s)
{
  if (!this)
    return;
  safe_free(&this->str);
  if (s)
    this->str = strdup(s);
}

String.h

#ifndef STRING_H_
# define STRING_H_

typedef struct  String
{
  char          *str;
  void          (*assign_s)(struct String *this, const struct String *str);
  void          (*assign_c)(struct String *this, const char *s);
  void		(*append_s)(String *this, const String *ap);
  void		(*append_c)(String *this, const char *ap);
}               String;

void StringInit(String *this, const char *s);
void StringDestroy(String *this);

#endif /* !STRING_H_ */