c语言字符串函数的实现

#include <stdio.h>
typedef char* string;

/**
字符串比较
**/
int strcmp(const char* src,const char* dest){
int ret = 0;
unsigned char* p1 = (unsigned char*)src;
unsigned char* p2 = (unsigned char*)dest;
while(!(ret = *p1 - *p2) && *p2){
++p1;
++p2;
}
if(ret < 0)
ret = -1;
else if(ret > 0)
ret = 1;
return ret;

}

/**
求字符串的长度
**/
unsigned strlen(const char* str){
int count = 0;
if(!str)
return 0;
for(;*str != '\0';++str){
++count;
}
return count;
}

/**
字符串拷贝
**/
char* strcopy(char *d, const char *s){
char *r=d;
while((*d++=*s++));
return r;
}

void main(){
string s = "hello world!";
string s2 = "hello !";
char s3[20];
printf("s=%s\n",s);
printf("len=%d\n",strlen(s));

printf("ret=%d\n",strcmp(s,s2));

strcopy(s3,s);
printf("s3 = %s",s3);
}