C++ 操作 LARGE_INTEGERS
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manipulating LARGE_INTEGERS
提问by Mick
I am converting some code from C to C++ in MS dev studio under win32. In the old code I was doing some high speed timings using QueryPerformanceCounter() and did a few manipulations on the __int64 values obtained, in particular a minus and a divide. But now under C++ I am forced to use LARGE_INTEGER because that's what QueryPerformanceCounter() returns. But now on the lines where I try and do some simple maths on the values I get an error:
我正在 win32 下的 MS dev studio 中将一些代码从 C 转换为 C++。在旧代码中，我使用 QueryPerformanceCounter() 进行了一些高速计时，并对获得的 __int64 值进行了一些操作，特别是减号和除法。但现在在 C++ 下，我被迫使用 LARGE_INTEGER，因为这是 QueryPerformanceCounter() 返回的内容。但是现在在我尝试对值进行一些简单的数学运算时，我得到了一个错误：
error C2676: binary '-' : 'LARGE_INTEGER' does not define this operator or a conversion to a type acceptable to the predefined operator
错误 C2676：二进制“-”：“LARGE_INTEGER”未定义此运算符或转换为预定义运算符可接受的类型
I tried to cast the variables to __int64 but then get:
我试图将变量强制转换为 __int64 但随后得到：
error C2440: 'type cast' : cannot convert from 'LARGE_INTEGER' to '__int64'
错误 C2440：“类型转换”：无法从“LARGE_INTEGER”转换为“__int64”
How do I resolve this?
我该如何解决？
Thanks,
谢谢，
回答by Jorge Ferreira
LARGE_INTEGER is a union of a 64-bit integer and a pair of 32-bit integers. If you want to perform 64-bit arithmetic on one you need to select the 64-bit int from inside the union.
LARGE_INTEGER 是一个 64 位整数和一对 32 位整数的联合。如果要对一个执行 64 位算术运算，则需要从联合内部选择 64 位 int。
LARGE_INTEGER a = { 0 };
LARGE_INTEGER b = { 0 };
__int64 c = a.QuadPart - b.QuadPart;
回答by Isaac
Here it is:
这里是：
LARGE_INTEGER x,y;
///
//Some codes...
///
__int64 diff = x.QuadPart - y.QuadPart
Because QuadPartis defined as a LONGLONG, that same as __int64.
因为QuadPart被定义为LONGLONG，与__int64相同。
回答by Cat Plus Plus
LARGE_INTEGERis a union, documented here. You probably want a QuadPartmember.
LARGE_INTEGER是一个联合，记录在此处。你可能想要一个QuadPart会员。
回答by jcopenha
LARGE_INTEGERis a union, you can still use .QuadPart if you want to work on the 64-bit value.
LARGE_INTEGER是一个联合，如果您想处理 64 位值，您仍然可以使用 .QuadPart。
回答by Mehdi
As the Documentationsays in the Remarkssection :
正如文档在备注部分所说：
The LARGE_INTEGERstructure is actually a union. If your compiler has built-in support for 64-bit integers, use the QuadPart member to store the 64-bit integer. Otherwise, use the LowPart and HighPart members to store the 64-bit integer.
该LARGE_INTEGER结构实际上是一个联合。如果您的编译器内置支持 64 位整数，请使用 QuadPart 成员来存储 64 位整数。否则，使用 LowPart 和 HighPart 成员来存储 64 位整数。
So if your compiler supports 64 bit integers use quadPart like this :
因此，如果您的编译器支持 64 位整数，请像这样使用 quadPart：
LARGE_INTEGER a, b;
__int64 diff = a.QuadPart - b.QuadPart
回答by M.Boelter
In addition to the answers, if you are looking to construct a LARGE_INTEGER with a value other than zero, you can assign the low and high parts separately. LowPart is first as defined in the union, and the only highPart is signed.
除了答案之外，如果您希望构造一个非零值的 LARGE_INTEGER，您可以分别分配低部分和高部分。LowPart 是联合中定义的第一个，并且唯一的 highPart 是有符号的。
LARGE_INTEGER li = {0x01234567, -1};
