两个无符号类型想减结果存储的临时变量还是无符号类型

#include <stdio.h>
int main()
{
    unsigned int dwVal = 0;
    unsigned __int64 n64Val = 1;
    if( dwVal - n64Val >= 20)
    {
        printf("%I64d\n",dwVal - n64Val);        //执行这行，输出 -1
    }
    return 0;
}

个人分析：

在做想减操作(dwVal - n64Val)时，会将dwVal和n64Val都转换为unsigned __int64,
两者想减的结果为-1，存储为0xFFFFFFFFFFFFFFFF,当成unsigned __int64使用
与 后面的数字(20)进行比较，所以计算结果为true，而打印输出的结果是 __int64类型
对应值为-1

进一步验证：

#include <iostream>
int main()
{
    unsigned int dwVal = 0;
    unsigned __int64 n64Val = 1;
    unsigned __int64 n64Val2 = 0xffffffffffffffff;
    if( dwVal - n64Val >= n64Val2)
    {
        printf("%I64d\n",dwVal - n64Val);        //执行这行，输出 -1
    }
    n64Val2 = dwVal - n64Val;        //n64Val2 = 0xffffffffffffffff
    system("pause");
    return 0;
}

#include <iostream>
int main()
{
    unsigned int dwVal = 0;
    unsigned __int64 n64Val = 2;
    unsigned __int64 n64Val2 = 0xffffffffffffffff;
    if( dwVal - n64Val >= n64Val2)
    {
        printf("%I64d\n",dwVal - n64Val);        //执行不到这里
    }
    n64Val2 = dwVal - n64Val;        //n64Val2 = 0xfffffffffffffffe,小于n64Val2
    system("pause");
    return 0;
}

有感于GetTickCount() 49.7天后计数置零

_LogTick = ::GetTickCount64();

    //DoSomething;

    if(::GetTickCount() - _LogTick >= LOG_TICK_MAX)
    {
        printf("%I64d\n",::GetTickCount() - _LogTick);
    }