c++ - manipulating LARGE_INTEGERS

Question

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:

error C2676: binary '-' : 'LARGE_INTEGER' does not define this operator or a conversion to a type acceptable to the predefined operator

I tried to cast the variables to __int64 but then get:

error C2440: 'type cast' : cannot convert from 'LARGE_INTEGER' to '__int64'

How do I resolve this?

Thanks,

Answer 1

LARGE_INTEGER 是一个 64 位整数和一对 32 位整数的并集。如果要对其中一个执行 64 位算术，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;

Answer 2

LARGE_INTEGER是一个工会，记录在这里。你可能想要一个QuadPart会员。

Answer 3

这里是：

LARGE_INTEGER x,y;
///
//Some codes...
///

__int64 diff = x.QuadPart - y.QuadPart

因为QuadPart被定义为LONGLONG，与__int64相同。

Answer 4

LARGE_INTEGER是一个联合，如果您想处理 64 位值，您仍然可以使用 .QuadPart。

Answer 5

正如文档在备注部分中所说：

该LARGE_INTEGER结构实际​​上是一个联合。如果您的编译器具有对 64 位整数的内置支持，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。

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

Answer 6

除了答案之外，如果您要构造一个非零值的 LARGE_INTEGER，您可以分别分配低和高部分。LowPart 首先是在联合中定义的，唯一的 highPart 是有符号的。

LARGE_INTEGER li = {0x01234567, -1};