When you make changes to your program, hoping to make it run faster, you need a way to accurately measure the time between certain events. You can do this by using the QueryPerformanceCounter and QueryPerformanceFrequency to measure this. As an example, lets use the following code:
Private Declare Function QueryPerformanceCounter Lib "kernel32"
(lpPerformanceCount As Any) As Long
Private Declare Function QueryPerformanceFrequency Lib "kernel32"
(lpFrequency As Any) As Long
'// timer frequency
Dim secFreq As Currency
Private Sub cmdTimeIt_Click()
Dim sec As Currency, secOut As Currency
Dim I As Long
'// start the timer
ProfileStart sec
'// do something
For I = 0 To 1000000
DoEvents
Next
ProfileStop sec, secOut
MsgBox secOut
End Sub
Sub ProfileStart(secStart As Currency)
'// if we do not have the timer frequency, then get it
If secFreq = 0 Then QueryPerformanceFrequency secFreq
'// get the current value
QueryPerformanceCounter secStart
End Sub
Sub ProfileStop(secStart As Currency, secTiming As Currency)
'// get the time passed
QueryPerformanceCounter secTiming
If secFreq = 0 Then
'// there is no high-resolution timer
available.
secTiming = 0
Else
'// calculate the time taken from
the start value, finish value, and the timer frequency.
secTiming = (secTiming - secStart)
/ secFreq
End If
End Sub
As you can see, we pass the ProfileStart procedure an empty Currency variable (sec) to hold the start value. When the code you want to run is finished, call the ProfileStop procedure with the start value (sec), and another empty Currency variable (secOut). The value contained in secOut is the time taken. You usually get the time taken, accurate to the nearest microsecond. As you can see, this is invaluable when trying to see the changes in performance as you change your code.
We can also use GetTickCount API for Measuring Performance. The following code
gives you an example.
Private Sub TimeOperation()
Dim I as Long
Dim x as Long
Dim Y as Long
Dim Z as Double
X = GetTickCount()
For I = 0 to 1000000
Z = SIN(i)
Next I
Y = GetTickCount - x
MsgBox "This operation takes " & Y/1000 &
" seconds to finish'
End Sub
Thanks to Georgi Ganchev for this tip.
For more information on this, and other methods for timing code, search for 'HOWTO: Use QueryPerformanceCounter to Time Code' in the MSDN library.
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