FAQs: 传值和传引用之间的区别是什么？
问题
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本帖的主题是：传值和传引用之间的区别是什么？
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答案
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当编写子程序或函数时，你可以将变量从主代码段传给他们。
如果你想通过ByVal语法来传递变量值：将变量的值传递过去而不是传引用，所有在自方法或函数中对此传入变量所作的改动都不会影响到主代码段。如果你不用ByVal或者ByRef对传入变量加以修饰的话，这是默认的传送机制。
如果你想将在自方法或函数中对传入变量所作改动返回到主代码段，则使用ByRef语法修饰传入变量。这将会传递对变量的引用并允变量值被修改并返回到主代码段。关于传值和传引用的传参方式的更多信息请参看MSDN文档：
http://msdn.microsoft.com/en-us/library/ddck1z30.aspx
请查看下面的代码段及其输出。代码声明了一个值类型变量和一个引用类型变量。然后将使用ByVal或ByRef关键词修饰的变量传送到不同子方法中：
Imports System.SecurityImports System.Security.Permissions
Imports System.IO
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles Button1.Click
Dim parameter_valtype As Integer = 10
Dim parameter_refertype As demo = New demo(1, "initial value")
Console.WriteLine("the value of value type variable parameter_valtype:" & _
parameter_valtype.ToString)
Console.WriteLine("pass value type variable parameter_valtype with byval modifier")
passByval_valType(parameter_valtype)
Console.WriteLine("the value of value type variable parameter_valtype:" & _
parameter_valtype.ToString)
Console.WriteLine("")
Console.WriteLine("pass value type variable parameter_valtype with byref modifier")
passByref_valType(parameter_valtype)
Console.WriteLine("the value of value type variable parameter_valtype:" & _
parameter_valtype.ToString)
Console.Write(vbCrLf)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.WriteLine("pass reference type variable parameter_valtype with byval modifier" & _
" and modify the reference variable ")
passByval_refType_modifyvarialble(parameter_refertype)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.Write(vbCrLf)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.WriteLine("pass reference type variable parameter_valtype with byval modifier")
passByval_refType(parameter_refertype)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.Write(vbCrLf)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.WriteLine("pass reference type variable parameter_valtype with byref modifier")
passByref_refType(parameter_refertype)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.Write(vbCrLf)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.WriteLine("pass reference type variable parameter_valtype with byref modifier" & _
" and modify the reference variable ")
passByref_refType_modifyvarialble(parameter_refertype)
Console.WriteLine("the value of reference type variable parameter_refype: " & _
parameter_refertype.nummember.ToString & " " & _
parameter_refertype.strmember)
Console.Write(vbCrLf)
End Sub
Public Sub passByref_valType(ByRef i As Integer)
i = i + 2
End Sub
Public Sub passByval_valType(ByVal i As Integer)
i = i + 4
End Sub
Public Sub passByval_refType(ByVal d As demo)
d.nummember = d.nummember * 2
d.strmember = "passByval_refType"
End Sub
Public Sub passByval_refType_modifyvarialble(ByVal d As demo)
d = New demo(11, "passByval_refType_modifyvarialble")
End Sub
Public Sub passByref_refType(ByRef d As demo)
d.nummember = d.nummember * 2
d.strmember = "passByref_refType"
End Sub
Public Sub passByref_refType_modifyvarialble(ByRef d As demo)
d = New demo(d.nummember * 2, "passByref_refType_modifyvarialble")
End Sub
End Class
Public Class demo
Private _strmember As String = String.Empty
Private _nummember As Integer = 0
Public Sub New(ByVal num As Integer, ByVal str As String)
_strmember = str
_nummember = num
End Sub
Public Property strmember() As String
Get
Return _strmember
End Get
Set(ByVal value As String)
_strmember = value
End Set
End Property
Public Property nummember() As Integer
Get
Return _nummember
End Get
Set(ByVal value As Integer)
_nummember = value
End Set
End Property
End Class
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- 已标记为答案 微软论坛技术支持团队 2011年3月2日 11:42
