The difference between ByVal and ByRef in VB

What is the difference between ByVal and ByRef in VB? In short, ByVal is the value, ByRef is the address, ByVal: Indicates that the parameter is passed by value. ByRef: Indicates that the parameter is passed by reference. The following green Tea Small series for you to introduce the difference between ByVal and ByRef.

1. The reference parameter (ref) can be passed as a reference parameter in a function member invocation. Must have been definitely assigned, and the output parameter (out) must not be definitely assigned before it can be passed as an output parameter in a function member invocation, before the function member returns normally.

2. Within a function, reference parameters (ref) are considered initially assigned, and output parameters (out) are considered initially unassigned.

3, by default, all the parameters in VB are value transfer. A reference pass is only explicitly contained in the modifier of a parameter, out or ref. But what you need to know is that when the type of the argument is a reference type, you pass a reference to an object instead of the actual object.

Instance:

Sub Add1 (ByVal No as Int32) no=no+100 End Sub Sub Add2 (ByRef No as Int32) no=no+100 End Sub Private Sub Button1_Click (sender as object,e as EventArgs) Handles Button1.Click Dim A As Int32 a=100 ADD1 (a) MsgBox ("A" value is: "& A)" shows: A has a value of 100 ADD2 (a) The value of MsgBox ("a": "& A") shows: A has a value of 200 because the parameter no in ADD2 is ByRef, that is, ' is delivered by address, so modifying the No in ADD2 will cause The value of the ' source parameter a ' is also modified. End Sub

ByVal is the Transfer value source data will not be modified, you can use this value as your own local variables; ByRef is the delivery address, the source data may be modified, your operation on this variable will affect the variable you pass in.