模擬實現C庫函數strcpy,strcat,strstr,strchr,strcmp,memcpy,memmove

1、模擬實現strcpy

char *my_strcpy( char *dest, const char *str)
{
	assert(dest != NULL);
	assert(str != NULL);
	while (*dest++=*str++)
	{
		;
	}
	return dest;
}
int main()
{
	char p[20];
	char *p1 = "world";
	my_strcpy(p, p1);
	printf("%s\n", p);
	system("pause");
	return 0;
}

2、模擬實現strcat

char* my_strcat(char*dest, const char* str)
{
	assert(dest != NULL);
	assert(str != NULL);
	char *ret = dest;
	while (*dest)
	{
		dest++;
	}
	while (*str)
	{
		*dest++ = *str++;
	}
	return ret;
}
int main()
{
	char p[20] = "hello ";
	my_strcat(p, "world");
	printf("%s", p);
	system("pause");
	return 0;
}

3、模擬實現strstr

char* my_strstr(const char *dest, const char*str)
{
	assert(dest != NULL);
	assert(str != NULL);
	char *ret = (char*)dest;
	char *cur = (char*)str;
	while (*cur)
	{
		if ((*ret) && (*cur) && (*ret++ = *cur++))
		{
			return cur;
		}
		cur++;
	}
	return NULL;
}

int main()
{
	char p[] = "abcdefd";
	char* p1 = "defr";
	char* ret = NULL;
	ret= strstr(p, p1);
	if (ret == NULL)
	{
		printf("no");
	}
	else
	{
		printf("%s", ret);
	}
	system("pause");
}

4、模擬實現strchr

char* my_strchr(const char*dest, int x)
{
	assert(dest != NULL);
	char*ret = (char*)dest;
	while (*ret)
	{
		if ((*ret) && (*ret == x))
		{
			return ret;
		}
		ret++;
	}
	return NULL;
}

int main()
{
	char p[] = "abcdefg";
	char*ret=my_strchr(p, 'f');
	if (ret == NULL)
	{
		printf("no\n");
	}
	else
	{
		printf("%s", ret);
	}
	system("pause");
	
}

5、模擬實現strcmp

int my_strcmp(const char*str1, const char*str2)
{
	assert(str1 != NULL);
	assert(str2 != NULL);
	while (*str1==*str2)
	{
		if (*str1 == '\0')
		{
			return 0;
		}
		*str1++;
		*str2++;
	}
	if (*str1 > *str2)
	{
		return 1;
	}
	else if (*str1 < *str2)
	{
		return -1;
	}
}

int main()
{
	char p1[] = "dccbcc";
	char p2[] = "dccccc";
	int ret = my_strcmp(p1, p2);
	printf("%d\n", ret);
	system("pause");
}

6、模擬實現memcpy

void*my_memcpy(void*dest, const void*str, size_t sz)
{
	assert(dest != NULL);
	assert(str != NULL);
	char* ret = (char*)str;
	char* cur = (char*)dest;
	while (sz--)
	{
		*cur++ = *ret++;
	}
	return dest;
}

int main()
{
	char p1[20] = { 0 };
	char* p2 = "world";
	my_memcpy(p1, p2, 4);
	printf("%s\n", p1);
	system("pause");
	return 0;
}

7、模擬實現memmove

void* my_memmove(void*dest, const void*str, size_t len)
{
	assert(dest != NULL);
	assert(str != NULL);
	char *pdest = (char*)dest;
	char* pstr = (char*)str;
	if ((pstr < pdest) && (pdest < pstr + len))
	{
		while (len--)
		{
			*(pdest+len) = *(pstr+len);
		}
	}
	else
	{
		while (len--)
		{
			*pdest++ = *pstr++;
		}
	}
	return dest;
}
int main()
{
	char p[] = "abcdefgh";
	my_memmove(p, p+2, 4);
	printf("%s", p);
	system("pause");
	return 0;
}