转载自http://blog.csdn.net/h971379154/article/details/48846755
//常见字符串操作函数内部实现
#include <stdio.h>
size_t strlen(const char *s)//char型指针间距可表示长度
{
const char *sc;
for (sc = s; *sc != '\0'; ++sc);
return sc - s;
}
char *strcpy(char *dest, const char *src)//将src字符串拷贝到dest字符串
{
char *tmp = dest;
while ((*dest++ = *src++) != '\0');
return tmp;
}
char *memset(char *s, int c, size_t count)//将字符串的前count个字符设置成字符c
{
char *xs = s;
while (count--)
*xs++ = c;
return s;
}
void *memcpy(char *dest, const char *src, size_t count)
{
char *tmp = dest;
const char *s = src;
while (count--)
*tmp++ = *s++;
return dest;
}
char * strcat(char * dest, const char * src) //连接字符串
{
char *tmp = dest;
while (*dest)
dest++;
while ((*dest++ = *src++) != '\0');
return tmp;
}
/*
若str1==str2,则返回零;
若str1>str2,则返回正数;
若str1<str2,则返回负数。
*/
int strcmp(const char *str1,const char *str2)
{
/*不可用while(*str1++==*str2++)来比较,当不相等时仍会执行一次++,
return返回的比较值实际上是下一个字符。应将++放到循环体中进行。*/
while(*str1 == *str2)
{
if(*str1 == '\0')
return 0;
str1++;
str2++;
}
return *str1 - *str2;
}
int main(void)
{
printf("%d\n",strlen("abchello"));
char *src = "blain";
char dest[10];
char *s="blain";
char pdest[10] ="goon";
printf("%s\n",strcat(pdest,s));
char *s1 = "abc";
char *s2 = "ab";
printf("%d\n",strcmp(s1,s2));
//printf("%s\n",strcpy(dest,src));
//printf("%s\n",memset(dest,'a',3));
printf("%s\n",memcpy(dest,src,6));
return 0;
}