库函数之字符函数与字符串函数(下)

#include <stdio.h>
#include <assert.h>
char* my_strncpy(char* strDest, const char* strSource, size_t count)
{
	assert(strDest);
	assert(strSource);
	char* ret = strDest;
	while (count--)
	{
		*strDest++ = *strSource++;
	}
	return ret;
}
int main()
{
	char arr1[20] = "xxxxxxxxxxxxxx";
	char arr2[] = "Hello CSDN!";
	int sz2 = sizeof(arr2) / sizeof(arr2[0]);
	printf("%s", my_strncpy(arr1,arr2,5));
	return 0;
}

#include <stdio.h>
#include <assert.h>
char* my_strncat(char* destination, const char* source, size_t num)
{
	assert(destination);
	assert(source);
	char* ret = destination;
	while (*destination != '\0')
	{
		destination++;
	}
	while (num--)
	{
		*destination++ = *source++;
	}
	return ret;
}

int main()
{
	char arr1[20] = "Hello ";
	char arr2[] = "CSDN!";
	int sz2 = sizeof(arr2) / sizeof(arr2[0]);
	printf("%s", my_strncat(arr1, arr2, 3));
	return 0;
}

#include <stdio.h>
#include <assert.h>
int my_strncmp(const char* str1, const char* str2, size_t num)
{
	while (num--)
	{
		if (*str1 > *str2)
		{
			return 1;
		}
		else if (*str1 < *str2)
		{
			return -1;
		}
		str1++;
		str2++;
	}
	return 0;
}
int main()
{
	char arr1[20] = "aabbccdd";
	char arr2[] = "aabbcdef";
	int sz2 = sizeof(arr2) / sizeof(arr2[0]);
	printf("%d", my_strncmp(arr1, arr2, 5));
	return 0;
}

int strStr(char * haystack, char * needle){
    char*ret=strstr(haystack,needle);
    if(ret-haystack<0)//小于0时,返回-1;
    {
        return -1;
    }
    return ret-haystack;
}

#include <stdio.h>
#include <assert.h>
char* my_strstr(const char* str1, const char* str2)
{
	assert(str1 && str2);
	if (*str2 == '\0')//如果子字符串是空字符串,直接返回主字符串
	{
		return str1;
	}
	const char *ret,*p1,*p2;
	ret = p1 = str1;
	p2 = str2;
	while (*p1&&*p2)//循环停止条件为主字符串或者子字符串有一个为空
	{
		if (*p1 == *p2)//相等则继续比较
		{
			p1++;
			p2++;
		}
		else//不相等则返回指定位置重新比较
		{
			p1 = ++ret;
			p2 = str2;
		}
	}
	if (*p2 == '\0')//如果子字符串比较结束,则匹配成功
	{
		return ret;
	}
	else//否则匹配失败
		return NULL;
}
int main()
{
	char str1[20] = "ABBCDABBACBBD";
	char str2[] = "ABBA";
	char* ret = my_strstr(str1, str2);
	if (ret == NULL)
	{
		printf("没有找到\n");
	}
	else printf("%s", ret);
}

#include <stdio.h>
#include <string.h>
int main()
{
	char str1[30] = "123.456.789_111,222@333";
	char str2[30];
	char a[] = "._,@";
	strcpy(str2, str1);//因为strtok函数会改变传过去的字符串的内容,所以我们是将备份传过去
	char* ret;
	//除了第一次调用时第一个参数为str2以外,后面的调用都是传入NULL,这样才会继续向后寻找标记分隔字符.
	for (ret = strtok(str2, a); ret != NULL; ret = strtok(NULL, a))
	{
		printf("%s\n", ret);
	}
	return 0;
}

#include <stdio.h>
#include <string.h>
int main()
{
	printf("%s\n", strerror(0));
	printf("%s\n", strerror(1));
	printf("%s\n", strerror(2));
	printf("%s\n", strerror(3));
	printf("%s\n", strerror(4));
	printf("%s\n", strerror(5));

	return 0;
}

#include <stdio.h>
#include <string.h>
#include <errno.h>

int main()
{
	//打开文件
	FILE* pf = fopen("CSDN.txt", "r");
	if (pf == NULL)
	{
		//printf("%s\n", strerror(errno));
		perror("fopen");
		return 1;
	}
	
	//关闭文件
	fclose(pf);
	pf = NULL;//避免空指针
	return 0;
}