之從寫出55ms解析度的計數器之後
就不斷去嘗試如何寫出以m sec或μsec
有一位來自《Experts-Exchange.com:zebada》提供一份資料
註釋的部份是我附加上去的，詳細的部份可參考MSDN
For an x86 platform I presume?
This code will get down to 1/3 of a microsecond if your motherboard has a
high frequency timer circuit on it. Most modern motherboards do.
Here's the code followed by the output:
#include <stdio.h>
#include <windows.h>
int main(int argc, char *argv[])
{
//The LARGE_INTEGER structure is used to represent
//a 64-bit signed integer value.
LARGE_INTEGER f,t1,t2,e;
double uf;
/*
Size Prefixes for printf and wprintf Format-Type Specifiers
To specify Use prefix With type specifier
__int64 I64 d, i, o, u, x, or X
*/
/*
The LARGE_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.
BOOL QueryPerformanceFrequency( LARGE_INTEGER* lpFrequency );
Parameters:lpFrequency
[out] Pointer to a variable that receives the current
performance-counter frequency, in counts per second.
*/
QueryPerformanceFrequency(&f);
printf("Frequency (counts per second) %I64d\n",f.QuadPart);
uf = f.QuadPart/1000000.0;
printf("Frequency (counts per microsecond) %lf\n",uf);
QueryPerformanceCounter(&t1);
Sleep(1000);
QueryPerformanceCounter(&t2);
e.QuadPart = (t2.QuadPart-t1.QuadPart);
printf("Elapsed counts %I64d\n",e.QuadPart);
printf("Elapsed microseconds %lf\n",e.QuadPart/uf);
return 0;
}
Frequency (counts per second) 3579545
Frequency (counts per microsecond) 3.579545
Elapsed counts 3580714
Elapsed microseconds 1000326.577819
If you want to get finer than this you may need to investigate the pentium
specific timestamp opcode - can't remember what it is - but it will measure
times in CPU clock cycles.
Regards
Paul
經過修改之後就可以得到大約0.28mSec解析度的計數器(測試環境VC6.0)
#include <stdio.h>
#include <conio.h> //for kbhit()
#include
int main(int argc, char *argv[])
{
LARGE_INTEGER f,start_count,end_count,elapse;
long int count_per_sec;
QueryPerformanceFrequency(&f);
count_per_sec = f.QuadPart;
QueryPerformanceCounter(&start_count);
for( ;!kbhit(); )
{
QueryPerformanceCounter(&end_count);
elapse.QuadPart = (end_count.QuadPart-start_count.QuadPart);
printf("Elapsed microseconds:%.6lf\r",elapse.QuadPart/(double)count_per_sec);
}
printf("\n");
return 0;
}
Elapsed microseconds:2.630882
Written By James On 2004/02/08