学步园

//字符串替换函数，在字符串 string 中查找 source， 找到则替换为destination，找不到则返回NULL
static char * replace_string (char * string, const char * source, const char * destination )
{
	char* sk = strstr (string, source);
	if (sk == NULL) return NULL;

	char* tmp;
	size_t size = strlen(string)+strlen(destination)+1;

	char* newstr = (char*)calloc (1, size);
	if (newstr == NULL) return NULL;

	char* retstr = (char*)calloc (1, size);
	if (retstr == NULL)
	{
		free (newstr);
		return NULL;
	}
	
	snprintf (newstr, size-1, "%s", string);
	sk = strstr (newstr, source);

	while (sk != NULL)
	{
		int pos = 0;
		memcpy (retstr+pos, newstr, sk - newstr);
		pos += sk - newstr;
		sk += strlen(source);
		memcpy (retstr+pos, destination, strlen(destination));
		pos += strlen(destination);
		memcpy (retstr+pos, sk, strlen(sk));

		tmp = newstr;
		newstr = retstr;
		retstr = tmp;

		memset (retstr, 0, size);
		sk = strstr (newstr, source);
	}
	free (retstr);
	return newstr;

}

//字符串插入函数  在字符串string 中查找 source ， 找到后再 source之后插入字符串 destination， 找不到则返回 NULL
static char * insert_string (char * string, const char * source, const char * destination )
{
	char* sk = strstr (string, source);
	if (sk == NULL) return NULL;
	char* tmp;
	size_t size = strlen(string)+strlen(destination)+1;
	char* newstr = (char*)calloc (1, size);
	if (newstr == NULL) return NULL;

	char* retstr = (char*)calloc (1, size);
	if (retstr == NULL)
	{
		free (newstr);
		return NULL;
	}
	
	snprintf (newstr, size-1, "%s", string);

	sk = strstr (newstr, source);

	int pos = 0;
	sk += strlen(source);

	memcpy (retstr+pos, newstr, sk - newstr);
	pos += sk - newstr;

	memcpy (retstr+pos, destination, strlen(destination));
	pos += strlen(destination);
	memcpy (retstr+pos, sk, strlen(sk));

	free (newstr);
	return retstr;

}