Como utilizar QueryPerformanceCounter para código de tempo

Function                 Units                      Resolution
---------------------------------------------------------------------------
Now, Time, Timer         seconds                    1 second
GetTickCount             milliseconds               approx. 10 ms
TimeGetTime              milliseconds               approx. 10 ms
QueryPerformanceCounter  QueryPerformanceFrequency  same
				

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Procedimentos passo a passo

1. Introduza o código seguinte para um módulo. Se introduzir numa classe, formulário ou módulo de relatório, efectue as declarações privada.

          Option Explicit
   
         Declare Function QueryPerformanceCounter Lib "Kernel32" _
                                    (X As Currency) As Boolean
         Declare Function QueryPerformanceFrequency Lib "Kernel32" _
                                    (X As Currency) As Boolean
         Declare Function GetTickCount Lib "Kernel32" () As Long
         Declare Function timeGetTime Lib "winmm.dll" () As Long
   
         Sub Test_Timers()
         Dim Ctr1 As Currency, Ctr2 As Currency, Freq As Currency
         Dim Count1 As Long, Count2 As Long, Loops As Long
         '
         ' Time QueryPerformanceCounter
         '
           If QueryPerformanceCounter(Ctr1) Then
             QueryPerformanceCounter Ctr2
             Debug.Print "Start Value: "; Format$(Ctr1, "0.0000")
             Debug.Print "End Value: "; Format$(Ctr2, "0.0000")
             QueryPerformanceFrequency Freq
             Debug.Print "QueryPerformanceCounter minimum resolution: 1/" & _
                         Freq * 10000; " sec"
             Debug.Print "API Overhead: "; (Ctr2 - Ctr1) / Freq; "seconds"
           Else
             Debug.Print "High-resolution counter not supported."
           End If
         '
         ' Time GetTickCount
         '
           Debug.Print
           Loops = 0
           Count1 = GetTickCount()
           Do
             Count2 = GetTickCount()
             Loops = Loops + 1
           Loop Until Count1 <> Count2
           Debug.Print "GetTickCount minimum resolution: "; _
                       (Count2 - Count1); "ms"
           Debug.Print "Took"; Loops; "loops"
         '
         ' Time timeGetTime
         '
           Debug.Print
           Loops = 0
           Count1 = timeGetTime()
           Do
             Count2 = timeGetTime()
             Loops = Loops + 1
           Loop Until Count1 <> Count2
           Debug.Print "timeGetTime minimum resolution: "; _
                       (Count2 - Count1); "ms"
           Debug.Print "Took"; Loops; "loops"
         End Sub
   						

2. Execute a função da janela Immediate/Debug. A saída deverá ser semelhante à seguinte:
   Inicie o valor: 3516284.3498
   Valor final: 3516284.3521
   Resolução mínima QueryPerformanceCounter: 1/1193182 seg
   Custos gerais de API: 1.92761875388667E - seconds 05
   
   Resolução mínima ObterContagemMarcaEscala: 10 ms
   Demorou 650 ciclos
   
   resolução mínima timeGetTime: 10 ms
   Demorou 1565 ciclos

   Private Sub Time_Addition()
   Dim Ctr1 As Currency, Ctr2 As Currency, Freq As Currency
   Dim Overhead As Currency, A As Long, I As Long
     QueryPerformanceFrequency Freq
     QueryPerformanceCounter Ctr1
     QueryPerformanceCounter Ctr2
     Overhead = Ctr2 - Ctr1        ' determine API overhead
     QueryPerformanceCounter Ctr1  ' time loop
     For I = 1 To 100
       A = A + I
     Next I
     QueryPerformanceCounter Ctr2
     Debug.Print "("; Ctr1; "-"; Ctr2; "-"; Overhead; ") /"; Freq
     Debug.Print "100 additions took";
     Debug.Print (Ctr2 - Ctr1 - Overhead) / Freq; "seconds"
   End Sub
				

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