exercise22

1.模拟实现strncpy

#include<stdio.h>
#include<assert.h>

int my_strncpy(char * dst, const char *src, size_t num)
{
	assert(dst);
	assert(src);
	char *ret = dst;
	while (num--)
	{
		*dst = *src;
		dst++, src++;
	}
	return ret;
}
int main()
{
	char src[20] = "1234567";
	char dst[20] = "abcdefg";
	printf("%s", my_strncpy(dst, src, 4));
	system("pause");
	return 0;
}

2.模拟实现strncat  

#include<stdio.h>
#include<assert.h>

char* my_strncat(char*dst, const char*src, size_t num)
{
	assert(dst);
	assert(src);
	char*ret = dst;
	while (*ret)
	{
		ret++;
	}
	while (num--)
	{
		*ret++ = *src++;
	}
	*ret = 0;
	return dst;
}
int main()
{
	char str1[10] = "hello";
	char str2[10] = "world";
	int len = strlen(str1);
	char *ret = my_strncat(str1, str2, len);
	printf("%s\n", ret);

	system("pause");
	return 0;
}

3.模拟实现strncmp

#include<stdio.h>
#include<assert.h>

int my_strncmp(const char*str1, const char*str2, size_t num)
{
	assert(str1);
	assert(str2);
	while (num--)
	{
		if (*str1 == *str2)
		{
			str1++;
			str2++;
		}
		else
		{
			if ((*str1 - *str2) < 0)
			{
				return -1;
			}
			else
				return 1;
		}
	}
	return 0;
}

int main(void)
{
	char *str1 = "abcd";
	char *str2 = "abcdefgh";
	int len = strlen(str2);
	int ret = my_strncmp(str1, str2, len);
	printf("%d\n", ret);
	system("pause");
}