字符串操作函数

//1.计数器的写法
//2.递归的写法
//3.指针-指针
#include <assert.h>
int my_strlen(const char* str)
{
	int count = 0;
	assert(str != NULL);
	while (*str != '\0')
	{
		count++;
		str++;

	}
	return count;
}

int main()
{
	int len = my_strlen("abcdef");//6
	//错误写入
	//char arr[] = { 'a','b','c','d','e','f' };//19,寻找\0，但是这种写入方式没有\0，只能是随机找，随机停止
	//int len = strlen(arr);

	printf("%d\n", len);
	return 0;
}

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

char* my_strcpy(char* dest, const char* src)
{
	assert(dest != NULL);
	assert(src != NULL);
	char* ret = dest;

	while (*src != '\0')//可以直接精简成这样while（*dest++ = *src++）
	{
		*dest = *src;
		dest++;
		src++;
	}
	*dest = *src;
	return ret;//返回目的空间的起始地址
}


int main()
{
	char arr1[] = { "abcdef" };
	char arr2[] = { "bit" };

	my_strcpy(arr1, arr2);
	printf("%s\n", arr1);
	return 0;
}

char *arr1 = "abcdefhi"，不是字符串数组，是一个常量字符串，无法修改

int main()
{
	char arr1[30] = { "Hello" };
	char arr2[] = { "World" };

	strcat(arr1, arr2);
	printf("%s\n", arr1);

	return 0;
}

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

char* my_strcat(char* dest,const char* src)
{
	char* ret = dest;
	assert(dest != NULL);
	assert(src != NULL);

	//找到目的字符串的'\0'
	while (*dest != '\0')
	{
		dest++;
	}
	while (*dest++ = *src++)
	{
		;
	}
	return ret;
}


int main()
{
	char arr1[30] = { "Hello" };
	char arr2[] = { "World" };

	my_strcat(arr1, arr2);
	printf("%s\n", arr1);

	return 0;
}

int main()
{
	char* p1 = "tbcdefhig";
	char* p2 = "sqwer";

	int ret = strcmp(p1, p2);
	printf("%d\n", ret);
	return 0;
}

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

int my_strcmp(const char* str1,const char* str2) 
{
	assert(str1 && str2);
	while (*str1 == *str2)
	{
		if (*str1 == '\0')
		{
			return 0;//相等
		}
		str1++;
		str2++;
	}
	if (*str1 > *str2)
	{
		return 1;//大于
	}
	else
		return -1;//小于

}



int main()
{
	char* p1 = "abcdef";
	char* p2 = "abcwer";

	int ret = my_strcmp(p1, p2);
	printf("%d\n", ret);
	return 0;
}

int main()
{
	char arr1[10] = { "abcdef" };
	char arr2[] = { "helloworld" };
	strncpy(arr1, arr2, 6);
	printf("%s\n", arr1);
	return 0;
}