程序打印错误的输出

Question

This program should print "SNP" but it prints "SNW".

#include <stdio.h> 
int main() { 
    int o = '!?zx' 
            ^ '!h4+'; 
    printf("%s\n", &o); 
    return (o ^ o); 
} 

Answer 1

I tried your program and got SNW .

As ^ is the XOR operation, I made it by hand and got the same result:

        Here is the problem
                |||
                VVV
 00100001 00111 111  01111010 01111 00   <- !?zx
 00100001 01101 000  00110100 00101011   <- !h4+
--------------------------------------- XOR
 00000000 01010 111  01001110 01011111   <- binary result
       00        57        4E       53   <- hexadecimal result
                  W         N        S   <- characters

Are you sure it would output SNP normally? The XOR operator between ? and h gives 00111111^01101000 which is 01010111 , or W in Unicode or ASCII. P is 01010000 .

So I marked the problematic bits above and put them below. The issue is that, it gives

the bits   111
before |   000
       V  ----- XOR
    01010  111

and 01010 111 makes W, instead of 01010 000 which would make P.

Also, due to endianness, you can get WNS as well as SNW .