自定义常用的字符串函数（strlen,strcpy,strcmp,strcat）

1、写一个函数将字符串倒叙输出

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

void func(char *src)
{
    int len = strlen(src);         // 获取字符串长度
    for(int i = 0; i < (len / 2); i++)
    {
        char tmp = src[i]; // 交换第i个和第len-1-i个字符
        src[i] = src[len - 1 - i];
        src[len - 1 - i] = tmp;
    }
    printf("%s\n", src);
}

int main(int argc, char const *argv[])
{
    char src[] = "abcde"; // 用字符数组存储，可修改
    func(src);            // 输出：edcba
    return 0;
}

2、写一段代码，判断当前是大端序还是小端序

#include <stdio.h>

int main()
{
	int a = 0x12345678;
	
	char *p=NULL;
	p=(char *)&a;
	
	printf("%#x\n",*p);
	
}

3、自己写的strlen()函数

#include <stdio.h>

unsigned long My_Strlen(char *s)
{
	if(s == NULL)
		return 0;
		
	unsigned long count = 0;
	while(*s != '\0')
	{
		s++;
		count++;
	}
	return count;
}

int main()
{
	char str[]={"wertyuiokjhdfghjjb vifnv"};
	
	unsigned long len=My_Strlen(str);
	
	printf("该字符串长度为：%ld\n",len);
	
}

4、自己写的strcpy()函数

#include <stdio.h>

void My_Strcpy(char *a,char *b)
{
	if((a == NULL)|| (b == NULL))
		return ;
	
	while(*b != '\0')
	{
		*a=*b;
		a++;
		b++;
	}
	*a='\0';
}

int main()
{
	char stra[]={"hello"};
	char strb[]={"world"};
	printf("stra：%s\n",stra);
	printf("strb：%s\n",strb);
	
	My_Strcpy(stra,strb);
	
	printf("stra复制到strb后：%s\n",stra);
	
}

5、自己写的strcat()函数

#include <stdio.h>

void My_Strcat(char *a,char *b)
{
	if((a == NULL)|| (b == NULL))
		return ;
	
	while(*a != '\0')
	{
		a++;
	}
	while(*b!='\0')
	{
		*a=*b;
		a++;
		b++;
	}
	*a='\0';
}

int main()
{
	char stra[]={"hello"};
	char strb[]={"world"};
	printf("stra：%s\n",stra);
	printf("strb：%s\n",strb);
	
	My_Strcat(stra,strb);

	printf("strb追加复制到stra后：%s\n",stra);
	
}

6、自己写的strcmp()函数

#include <stdio.h>

int My_Strcmp(char *a,char *b)
{
	if((a == NULL)|| (b == NULL))
		return -99;
	
	while((*a != '\0')&& (*b!='\0') && (*a == *b))
	{
		a++;
		b++;
	}
	return *a-*b;
}

int main()
{
	char stra[]={"hello"};
	char strb[]={"hellp"};
	printf("stra：%s\n",stra);
	printf("strb：%s\n",strb);
	
	int x=My_Strcmp(stra,strb);

	printf("stra与strb进行strcmp后=%d\n",x);
	
}