有人可以解释 GCC-7 编译器的以下行为吗?
// main.cpp
#include <iostream>
using namespace std;
int main()
{
int a = -2147483648;
int b = -a;
cout << "a == " << dec << a << " == 0x" << hex << a << "\n";
cout << "b == " << dec << b << " == 0x" << hex << b << "\n";
if (a > 0)
cout << "a > 0 // ERROR\n";
else
cout << "a <= 0 // OK\n";
if (b > 0)
cout << "b > 0 // ERROR\n\n";
else
cout << "b <= 0 // OK\n\n";
int aa[] = { -2147483648, 0 };
int bb = -aa[0];
cout << "aa[0] == " << dec << aa[0] << " == 0x" << hex << aa[0] << "\n";
cout << "bb == " << dec << bb << " == 0x" << hex << bb << "\n";
if (aa[0] > 0)
cout << "aa[0] > 0 // ERROR\n";
else
cout << "aa[0] <= 0 // OK\n";
if (bb > 0)
cout << "bb > 0 // ERROR\n\n";
else
cout << "bb <= 0 // OK\n\n";
cin.get();
return 0;
}
未经优化的编译:g++ main.cpp
输出:
a == -2147483648 == 0x80000000
b == -2147483648 == 0x80000000
a <= 0 // OK
b <= 0 // OK
aa[0] == -2147483648 == 0x80000000
bb == -2147483648 == 0x80000000
aa[0] <= 0 // OK
bb <= 0 // OK
优化编译:g++ -O2 main.cpp
输出:
a == -2147483648 == 0x80000000
b == -2147483648 == 0x80000000
a <= 0 // OK
b <= 0 // OK
aa[0] == -2147483648 == 0x80000000
bb == -2147483648 == 0x80000000
aa[0] <= 0 // OK
bb > 0 // ERROR
这是未定义的行为还是编译器错误?
GCC版本:gcc(Ubuntu 7.3.0-27ubuntu1~18.04)7.3.0
最佳答案
这是未定义的行为。大概在你的机器上int
是32位的,其范围是-2147483648
到2147483647
。尝试否定 -2147483648
会导致溢出(不是堆栈溢出:P),这是未定义的行为(定义了无符号溢出,但没有定义有符号溢出。)因此编译器可以做任何它喜欢的事情。
关于c++ - 比较 -INT_MIN (GCC),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52679742/