The importance of using byref/byval differently under. Net

Difference

All along, in VB6, parameters are routed by ByRef (that is, delivered by address).

Under. Net (c#,vb.net), parameters are routed by default using ByVal (that is, by value) and have not been noticed.

These days the optimizer found that using the default method (ByVal) is quite inefficient when transferring large variables

such as the incoming parameter variable type is a large string, array, collection, DataSet, etc.

The key code of the test is as follows, the string I passed in is not particularly large, the larger the variable, the higher the use of byref, of course, when the incoming variable can be modified or no other effect, you can switch to ByRef

Private Declare Function gettickcount Lib "kernel32" () as Int32

Private Function testbyref (ByRef AA As String) as String
AA = "1" & AA
Testbyref = AA

End Function

Private Function testbyval (ByVal AA As String) as String
AA = "1" & AA
Testbyval = AA

End Function

Private Sub button1_click (ByVal sender as System.Object, ByVal e as System.EventArgs) Handles Button1.Click

Dim Teststr as String
Dim Newstr as String

Dim T as Int32
Dim II as Int32

Teststr = "WOSDFSDFDSFDSFSFDSFSFSFSFSFSFDSFDSFCVXCVXCVCXVVCXVVVXVCVXV"

t = GetTickCount

For II = 1 to 10000
Newstr = Testbyref (TESTSTR)
Next

MsgBox ("ByRef" & CStr (GETTICKCOUNT-T))

t = GetTickCount

For II = 1 to 10000
Newstr = Testbyval (TESTSTR)
Next

MsgBox ("ByVal" & CStr (GETTICKCOUNT-T))

End Sub