c++ - unsigned long 大于 0xFFFFFFFF

Question

如果 unsigned long 最大值为 4294967295，测试程序如何得出 4294967297？

#include <iostream>
using namespace std;
unsigned long millis_diff(unsigned long then, unsigned long now) {
    return now < then ? now + then : now - then;
}
int main()
{
    unsigned long now = 2;
    unsigned long then = 4294967295; //unsigned long maximum value
    unsigned long diff = millis_diff(then, now);
    cout << diff;
    return 0;
}

Answer 1

原因是编译器定义 unsigned long int 的方式似乎与定义 unsigned long long int 的方式相同。:)

这是一个演示程序

#include <iostream>
#include <limits>

int main()
{
    std::cout << "sizeof( unsigned long ) = " << sizeof( unsigned long ) << '\n';
    std::cout << "The maximum values is " << std::numeric_limits<unsigned long>::max() << '\n';
}

它的输出是

sizeof( unsigned long ) = 8
The maximum values is 18446744073709551615