*s2 && !(*s1 - *s2) 这个什么意思

Question

#include <stdio.h>
char *LookFor_Str(char *RxBuffer,char *RxData);
int main()
{
    char *p;
    p=LookFor_Str("123","2");
    printf("%s\n",p);
    return 0;
}
char *LookFor_Str(char *RxBuffer,char *RxData)
{
   char *cp =(char *)RxBuffer;
   char *s1,*s2;
    if (!*RxData)
        return((char *)RxBuffer);
    while (*cp)
    {
        s1 = cp;
        s2 = (char *)RxData;
        while (***s2 && !(*s1 - *s2))**
            s1++,s2++;
        if (!*s2)
            {
            return cp;
            }
        cp++;
    }
      return "fail";
}

Answer 1

while (*s2 && !(*s1 - *s2))
    s1++, s2++;

等价于

while (*s2 != '\0' && *s1 == *s2) {
    s1++;
    s2++;
}

这段代码的意思是比较s1, s2两个字符串直到s2结尾或遇到不同的字符。