问题要求使用指针返回字符串的一部分

Question

int main (void)
{
char c[] = "KATEWINCE";
char *p =c;
printf("%s", p+p[3]-p[1]) ;
return (0);
}

The output is WINCE but I don't get how the code is working, please explain.

Answer 1

You assigned 0x45 to c[3] / p[3] . ^[1]

You assigned 0x41 to c[1] / p[1] . ^[1]

So p + p[3] - p[1] is equivalent to p + 0x45 - 0x41 .

This attempts to advance p by 0x45 elements. This is undefined behaviour. You can advance a pointer to the position immediately following the object to which it points, but no further. c is simply not that large.

But let's say c was far larger. You would see the same result as you posted here.

p is advanced by 0x45 elements, then reversed by 0x41 elements. The net result is that p is advanced by 4 elements. And that's exactly what we see.

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1. Assuming an ASCII-based machine.