【C深度剖析】自实现 strcmp strlen strcpy strcat

int str_cmp(const char *s1,const char *s2){        int ret;        while(!(ret = *(unsigned char *)s1 - *(unsigned char *)s2) && s2++)          s1++,s2++;        if(ret > 0)                ret = 1;        else if(ret <0)          ret = -1;                return ret;}int str_len(const char *s){        assert(s != 0);        char *start = s;        while(*s++);        return (s - start - 1);}char* str_cpy(char *dest,char *src){        assert( (dest != 0) && (src != 0));        char* ret = dest;        while(*src)          *dest++ = *src++;        *dest = '\0';        return ret;}char* str_cat(char *dest,char *src){        assert((dest != 0) && (src != 0));        char *ret = dest;        while(*dest)          dest++;        while(*src)          *dest++ = *src++;        *dest = '\0';        return ret;}