unsigned int类型的函数返回负数 [英] Function of type unsigned int returns negative number

问题描述

哇我以为我认识我的C ++，但这是奇怪的

Wow I thought I knew my C++ but this is weird

这个函数返回一个unsigned int，所以我认为这意味着我永远不会得到一个负数返回吗？

This function returns an unsigned int so I thought that means I will never get a negative number returned right?

该函数确定UTC前面或后面多少小时。所以对我来说，我在澳大利亚，悉尼，所以我是+10 GMT，这意味着我是UTC = LocalTime +（-10）。因此，GetTimeZoneInformation正确地确定我是-10。

The function determines how many hours ahead or behind of UTC you are. So for me I'm in Australia, Sydney so I am +10 GMT which means I am UTC = LocalTime + (-10). Therefore the GetTimeZoneInformation correctly determines I am -10.

但是我的函数返回一个unsigned int，所以不应该返回10不是-10？

unsigned int getTimeZoneBias()
{
    TIME_ZONE_INFORMATION tzInfo;
    DWORD res  = GetTimeZoneInformation( &tzInfo );

    if ( res == TIME_ZONE_ID_INVALID )
    {
        return (INT_MAX/2); 
    }

    return (unsigned int(tzInfo.Bias / 60));  // convert from minutes to hours         
}

TCHAR ch[200];
_stprintf( ch, _T("A: %d\n"), getTimeZoneBias()); // this prints out A: -10
debugLog += _T("Bias: ") + tstring(ch) + _T("\r\n");

推荐答案

以下是我的想法：

tzInfo.Bias 的值实际上为-10。 （ 0xFFFFFFF6 ）
在大多数系统上，将带符号的整数转换为大小相同的无符号整数对表示无效。

The value of tzInfo.Bias is actually -10. (0xFFFFFFF6) On most systems, casting a signed integer to an unsigned integer of the same size does nothing to the representation.

因此，函数仍然返回 0xFFFFFFF6 。

'重新打印为一个有符号整数。所以它打印 -10 。如果您将它作为无符号整数打印，则可能会得到 4294967286 。

But when you print it out, you're printing it back as a signed integer. So it prints-10. If you printed it as an unsigned integer, you'll probably get 4294967286.

要做的是得到时间差的绝对值。所以你想把这个-10转换成10.你应该返回 abs（tzInfo.Bias / 60）。

What you're probably trying to do is to get the absolute value of the time difference. So you want to convert this -10 into a 10. In which you should return abs(tzInfo.Bias / 60).

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