How to get the memory address of the variable in Visual Basic (Address of Variables)
This article is suitable for
Microsoft Visual Basic Learning Edition for Windows, Versions 5.0, 6.0
Microsoft Visual Basic Professional Edition for Windows, Versions 5.0, 6.0
Microsoft Visual Basic Enterprise Edition for Windows, Versions 5.0, 6.0
Summary
Little VB programmers need to get low-level information of a variable, such as memory addresses. However, some API functions require this
Information, the methods described herein can help VB programmers get this information
VarPtr - Returns the address of a variable return address of a variable VarPtrArray -.. Returns the address of an array return array address StrPtr -. Returns the address of the UNICODE string buffer returns UNICODE string buffer address VarPtrStringArray - Returns the address of an Array of strings. Returns a string array address Objptr - returns the pointer to the interface referened by an Object variable. Returns an object's interface reference pointer
text
Varptr
This function is used to get a variable or an array of addresses, pass a variable name or array and return the address. However, you have to understand that the dynamic array may be reassigned by VB, so you must be careful when you use Varptr to get an array of addresses.
Dim lngvariableaddress as long
DIM DBLMYVARIABLE AS DOUBLE
LNGVARIABLEADDRESS = VARPTR (dblmyvariable)
Dim LngelementAddress as long
Dim LNGARRAYOFLONGS (9) As long
'Following Will Get Address of 4th Element
LNGELEMENTADDRESS = Varptr (LNGARRAYOFLONGS (3))
Limit: This function cannot be used to obtain an address of the array
Varptrarray
When the array is in the Visual Basic to save the SafeArRays structure, you have to get the address of the SafearRays structure, you want to use the Varptrarray function, below the definition of VB5, VB6, respectively:
DECLARE FUNCTION VARPTRARRAY LIB "msvbvm50.dll" Alias "Varptr" _
(Var () as any) as long
DECLARE FUNCTION VARPTRARRAY LIB "msvbvm60.dll" Alias "Varptr" _
(Var () as any) as long
Dim LngsafeArrayaddress as long
Dim LNGARRAYOFLONGS (9) As long
LNGSAFEARRAYADDRESS = VARPTRARRAY (LNGARRAYOFLONGS ())
Limitation: The Varptrarray function cannot be used to obtain an address of a string array because VB will make Unicode / ANSI conversion for the string. If you use Varptrarray for the string array, you will get an address of a temporary ANSI array copy. Strptr
String first character of the first character DIM LNGCHARADDRESS AS Long
DIM STRMYVARIABLE AS STRING
Strmyvariable = "some string"
LNGCharaddress = strptr (strmyvariable)
This function can be used when you need to pass a Unicode string pointer in the API call
VarptrstringArray
VarptrstringArray is used to obtain the address of the string array. In order to avoid VB for Unicode / ANSI conversion,
Its statement must be defined in the type library
You can also use the MIDL compiler to compile the following .odl files into your own type library :) If it is Visual Basic 5.0, create a text file name to vb6ptrlib.odl, the content is as follows:
#define rtcall_stdcall
[
UUID (C6799410-4431-11D2-A7F1-00A0C91110C3),
LCID (0), Version (6.0), Helpstring ("VarptrstringArray Support for VB6)
]
Library Ptrlib
{
Importlib ("stdole2.tlb");
[Dllname ("MSVBVM60.DLL")]]]]
Module ArrayPtr
{
[Entry ("Varptr")]]]]
Long RTCall VarptrstringArray ([in] SafeArray (BSTR) * PTR);
}
}
If it is Visual Basic 5.0, create a text file name is VB5Ptrlib.odl, the content is as follows:
#define rtcall_stdcall
[
UUID (6E814F00-7439-11D2-98D2-00C04FAD90E7),
LCID (0), Version (5.0), Helpstring ("VarptrstringArray Support for VB5)
]
Library Ptrlib
{
Importlib ("stdole2.tlb");
[Dllname ("msvbvm50.dll")]]]]
Module ArrayPtr
{
[Entry ("Varptr")]]]]
Long RTCall VarptrstringArray ([in] SafeArray (BSTR) * PTR);
}
}
Compile the .odl file to build a VB5 or VB6 type library (.tlb) in the command line.
MIDL / T VB6PTRLIB.ODL
MIDL / T VB5PTRLIB.ODL
In order to use VarptrstringArray, you need to reference this type library.
example:
Dim MyArrayofstrings (2) AS STRING
Dim AddressofArray As Long
MyArrayofstrings (0) = "AAA"
MyArrayofstrings (1) = "BBB"
AddressofArray = VarptrstringArray (MyArrayofstrings ())
Objptr
Objptr returns an address of an Object variable
Objcollection.add myobj1, cstr (Objptr (myobj1)) ...
Objcollection.remove CSTR (Objptr (myobj1))
