ULARGE_INTEGER Union
The ULARGE_INTEGER structure is used to specify a 64-bit unsigned integer value.
typedef union _ULARGE_INTEGER {
struct {
DWORD LowPart;
DWORD HighPart;
};
struct {
DWORD LowPart;
DWORD HighPart;
} u;
ULONGLONG QuadPart; } ULARGE_INTEGER,
*PULARGE_INTEGER;
Members
- LowPart
-
Low-order 32 bits.
- HighPart
-
High-order 32 bits.
- u
- LowPart
-
Low-order 32 bits.
- HighPart
-
High-order 32 bits.
- QuadPart
-
Unsigned 64-bit integer.
Remarks
The ULARGE_INTEGER structure 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.
Header |
Declared in Winnt.h; include Windows.h |
---|
上面是MSDN上的說明!
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由於在32位PC上無法int最大值爲2^32,所以,對於64位數的存放採取了這樣一種數據結構,假如我們要對這個64位的數字進行運算的話應該怎麼辦呢?
例如 使用BOOL GetDiskFreeSpaceEx() 獲得磁盤信息時候
PULARGE_INTEGER FreeBytesAvailableToCaller;
……
BOOL GetDiskFreeSpaceEx(
LPCWSTR lpDirectoryName,
PULARGE_INTEGER lpFreeBytesAvailableToCaller,
PULARGE_INTEGER lpTotalNumberOfBytes,
PULARGE_INTEGER lpTotalNumberOfFreeBytes
)
獲取了磁盤空間之後,由於得到的值是以字節爲單位的,這裏,我們想將其轉化爲以G爲單位的。。
方法1:
(float)FreeBytesAvailableToCaller。HighPart<<2+(float)FreeBytesAvailableToCaller。LowPart/(1024*1024*1024);
原理: 首先,在計算機中所有數字都是以二進制存儲的,HighPart是高32位,LowPart是低32位,摒棄你腦袋裏的10進制概念,將這兩部分均以2進制的視角來看。。。1G是2^30字節,所以低32位再除以2^30後,低32位的高2位仍未改變(切記是二進制的視角)。。同理,高32位的每位在計算後也肯定不會改變,即30位以後的都不作改變,所以將30位之後的所有二進制位整合,就可以得到整個64位數除以2^30的二進制整數部分結果了,這裏(float)FreeBytesAvailableToCaller。HighPart<<2即空出倆位與後32位的高2位整合(HighPart<<2可以用*4代替)。。。
方法2:(float)FreeBytesAvailableToCaller。.QuadPart/(1024*1024*1024)直接計算。。。