the same equation on gcc or vs2022 have different result-CodePudding

int main()
{
    int y=2147483647;
    printf("%d\n",!(~y ~y));
}

When i compile it by gcc and run it in ubuntu, the result is 0.but when i compile and run it on vs2022,the result is 1. I can not understand how did the result of 0 come about.

CodePudding user response：

The bitwise inverse of decimal value 2147483647/0x7FFFFFFF will end up as 0x80000000. On a 2's complement system like yours, this is equivalent to -2147483648.

-2147483648 -2147483648 gives an arithmetic underflow of signed int, it's undefined behavior and anything can happen. In practice, during optimization the compiler can either make the decision that ~y ~y equals zero or that it equals non-zero, it's not well-defined.

Fix this by switching all types to int64_t/PRIi64 (#include <inttypes.h>).