【C语言字符函数和字符串函数(二)】--strcmp，strstr的使用和模拟实现，strncpy，strncat，strncmp函数的使用，strock，strerror函数的使用

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

int main()
{
	char arr1[] = "abcdef";
	char arr2[] = "abcd";
	int ret=strcmp(arr1, arr2);//strcmp中直接放字符串也可以比
	if (ret > 0)
		printf("arr1 > arr2\n");
	else if (ret < 0)
		printf("arr1 < arr2\n");
	else
		printf("arr1 == arr2\n");
	return 0;
}

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

int my_strcmp(const char* arr1, const char* arr2)
{
	assert(arr1 && arr2);
	while (*arr1 == *arr2)
	{
		if (*arr1 == '\0')
		{
			return 0;
		}
		arr1++;
		arr2++;
	}
	if (*arr1 > *arr2)
	{
		return 1;
	}
	else
		return -1;
}

int main()
{
	char arr1[] = "abcdef";
	char arr2[] = "abcdefg";
	int p=my_strcmp(arr1, arr2);
	if (p > 0)
	{
		printf("arr1>arr2");
	}
	else if (p < 0)
	{
		printf("arr1<arr2");
	}
	else
	{
		printf("arr1==arr2");
	}
	return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	char arr1[] = "heheabcdefabcdef";
	char arr2[] = "def";
	char* p = strstr(arr1, arr2);
	if (p != NULL)
		printf("找到了，%s\n", p);
	else
		printf("找不到\n");
}

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

char* my_strstr(const char* str1, const char* str2)
{
	assert(str1 && str2);
	char* p = (char*)str1;
	char* s1 = NULL;
	char* s2 = NULL;

	if (*str2 == '\0')
		return (char*)str1;

	while (*p)
	{
		s1=p;
		s2 = (char*)str2;
		while(*s1&&*s2&&*s1==*s2)
		{
			s1++;
			s2++;
		}

		if (*s2 == '\0')
			return p;
		
		p++;
	}

}
int main()
{
	char arr1[] = "abcdefg";
	char arr2[] = "def";
	char* ret = my_strstr(arr1, arr2);
	if (ret != NULL)
	{
		printf("找到了：%s", ret);
	}
	else
	{
		printf("找不到");
	}
	
	return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	char arr1[20] = { 0 };
	char arr2[] = "hello,world";
	char*p=strncpy(arr1, arr2,5);
	printf("%s\n", p);
	printf("%s\n", arr1);
	//两种打印方式都可以
	return 0;
}

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

char* my_strncpy(char* arr1, const char* arr2, size_t num)
{
	assert(arr1 && arr2);
	char* p = arr1;
	int i = 0;
	for (i = 0;i < num && arr2[i];i++)
	{
		arr1[i] = arr2[i];
	}
	if (i < num)
	{
		arr1[i] = 0;
	}
	return p;

}

int main()
{
	char arr1[20] = { 0 };
	char arr2[] = "abcdefg";
	char* ret = my_strncpy(arr1, arr2, 3);
	printf("%s", ret);
	return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	char arr1[20] = "hello";
	char arr2[] = "world";
	char*p=strncat(arr1, arr2,5);
	printf("%s\n", p);
	printf("%s\n", arr1);
	//两种打印方式都可以
	return 0;
}

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

char* mystrncat(char* arr1, const char*arr2 , size_t num)
{
	assert(arr1 && arr2);
	char* p = arr1;
	while (*arr1)
	{
		arr1++;
	}//找到目标字符串中的\0，明确从那里开始追加。
	int i = 0;
	for (i = 0;arr2[i] && i < num;i++)
	{
		arr1[i] = arr2[i];
	}
		arr1[i] = 0;
	return p;
}
int main()
{
	char arr1[20] = "hello";
	char arr2[] = "world";
	char* ret = mystrncat(arr1, arr2,3);
	printf("%s", ret);
	return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	char arr1[] = "abcdef";
	char arr2[] = "abcdqw";
	int ret=strncmp(arr1, arr2,5);
	if(ret>0)
	  printf(">\n");
	else if(ret<0)
	  printf("<\n");
	else
	  printf("=\n");
	return 0;
}

#include<stdio.h>
#include<string.h>
int main()
{
	char arr[] = "huangqirui@yuan.com";
	const char* sep = "@ .";//将@和.作为分隔符
	const char* str = NULL;

	char buf[30] = { 0 };
	strcpy(buf, arr);
	//将arr中的字符串拷贝到buf中，对buf的内容进行切割
	for (str = strtok(buf, sep);str != NULL;str = strtok(NULL, sep))
	{
		printf("%s\n", str);
	}
	return 0;
}

#include <errno.h>
#include <string.h>
#include <stdio.h>
//我们打印⼀下0~10这些错误码对应的信息
int main()
{
	int i = 0;
	for (i = 0; i <= 10; i++) {
		printf("%d.%s\n",i, strerror(i));
	}
	return 0;
}

#include <stdio.h>
#include <string.h>
#include <errno.h>
int main()
{
	//C语言可以打开文件
	//fopen
	//如果以读的形式打开文件，文件是必须要存在的，如果文件不存在，则打开文件失败
	//fopen函数就会将错误码放在errno
	//同时函数就会返回NULL
	FILE* pFile;
	pFile = fopen("unexist.ent", "r");
	if (pFile == NULL)
		printf("Error opening file unexist.ent: %s\n", strerror(errno));
	return 0;
}

#include <stdio.h>
#include <string.h>
#include <errno.h>
int main()
{
	FILE* pFile;
	pFile = fopen("unexist.ent", "r");
	if (pFile == NULL)
		perror("Error opening file unexist.ent");
	return 0;
}