VB中清除变量
(2010-11-24 09:46:10)
标签:
杂谈 |
分类: QTP/VBS20100524 |
资料来源于网络
变量一但定义,就会在程序执行在内存开辟出相应的空间,清除变量除非程序重新定义变量,重新加载,但这不可能实现。 楼上说的是重置变量,即刚定义的初值,如: 字符变量为"" 数值变量为0 布尔变量为False 对象变量可以Set 变量名=Nothing(如数据库对象)
sub里面的变量在sub执行完后自动就清空了!
1、定义对象变量可以加New,定义其它变量不能加New
2、你理解的基本正确,其实就是要释放对象变量所占的内存空间需要set nothing
3、VB下有指针,只是不提倡使用罢了,所以VB的帮助没有提到指针。
Function printAB
'
'
Print a
Print b
End Function
Print "--Test dim"
PrintAB
Print "Print the dim outside the function"
print a
print b
' Output log
'--Test dim
'10
'abc
'--Print the dim outside the function
Assigns an object reference to a variable or property, or associates a procedure reference with an event.
Set objectvar = {objectexpression | New classname | Nothing}
-or-
Set object.eventname = GetRef(procname)
Parameters
- objectvar
- Required. Name of the variable or property; follows standard variable naming conventions.
- objectexpression
- Optional. Expression consisting of the name of an object, another declared variable of the same object type, or a function or method that returns an object of the same object type.
- New
- Keyword used to create a new instance of a class. If objectvar contained a reference to an object, that reference is released when the new one is assigned. The New keyword can only be used to create an instance of a class.
- classname
- Optional. Name of the class being created. A class and its members are defined using the Class statement.
- Nothing
- Optional. Discontinues association of objectvar with any specific object or class. Assigning objectvar to Nothing releases all the system and memory resources associated with the previously referenced object when no other variable refers to it.
- object
- Required. Name of the object with which event is associated.
- event
- Required. Name of the event to which the function is to be bound.
- procname
- Required. String containing the name of the Sub or Function being associated with the event.
Remarks
To be valid, objectvar must be an object type consistent with the object being assigned to it.
The Dim, Private, Public, or ReDim statements only declare a variable that refers to an object. No actual object is referred to until you use the Set statement to assign a specific object.
Generally, when you use Set to assign an object reference to a variable, no copy of the object is created for that variable. Instead, a reference to the object is created. More than one object variable can refer to the same object. Because these variables are references to (rather than copies of) the object, any change in the object is reflected in all variables that refer to it.
Function ShowFreeSpace(drvPath) Dim fso, d, s Set fso = CreateObject("Scripting.FileSystemObject") Set d = fso.GetDrive(fso.GetDriveName(drvPath)) s = "Drive " & UCase(drvPath) & " - " s = s & d.VolumeName & "<BR>" s = s & "Free Space: " & FormatNumber(d.FreeSpace/1024, 0) s = s & " Kbytes" ShowFreeSpace = s End Function
Using the New keyword allows you to concurrently create an instance of a class and assign it to an object reference variable. The variable to which the instance of the class is being assigned must already have been declared with the Dim (or equivalent) statement.
Refer to the documentation for the GetRef function for information on using Set to associate a procedure with an event.
Returns a reference to a procedure that can be bound to an event.
Set object.eventname = GetRef(procname)
Arguments
- object
- Required. Name of the object with which event is associated.
- event
- Required. Name of the event to which the function is to be bound.
- procname
- Required. String containing the name of the Sub or Function procedure being associated with the event.
Remarks
The GetRef function allows you to connect a VBScript procedure (Function or Sub) to any available event on your DHTML (Dynamic HTML) pages. The DHTML object model provides information about what events are available for its various objects.
In other scripting and programming languages, the functionality provided by GetRef is referred to as a function pointer, that is, it points to the address of a procedure to be executed when the specified event occurs.
The following example illustrates the use of the GetRef function.
<SCRIPT LANGUAGE="VBScript"> Function GetRefTest() Dim Splash Splash = "GetRefTest Version 1.0" & vbCrLf Splash = Splash & Chr(169) & " YourCompany 1999 " MsgBox Splash End Function Set Window.Onload =GetRef(
"GetRefTest")
</SCRIPT>