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How to declare and use a DLL/API procedure

How to declare and use a DLL/API procedure

API Declarations


Alias "SetWindowTextA" (ByVal hwnd As Long, _
ByVal lpString As String) As Long





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'procedures in an external DLL or API in Visual Basic.

'•-- Declaring a DLL Procedure
'•-- The first step is to declare the procedure in the Declarations section of 
'    a module:
'    •-- You can find the exact syntax for a procedure by using the API Viewer 
'    •-- application, or by searching the Win32api.txt file. If you place the  Declare 
'    •-- in a Form or Class module, you must precede it with the Private keyword. 
'    •-- You declare a DLL procedure only once per project. You can then call it 
'    •-- any number of times.
    
'    •-- Calling a DLL Procedure:
'    •-- After the function is declared, you call it just as you would a standard 
'    •-- Visual Basic function. Here, the procedure has been attached to the 
'    •-- Form Load event:
    Private Sub Form_Load()
     SetWindowText Form1.hWnd, "Welcome to VB"
    End Sub
'    •-- When this code is run, the function first uses the hWnd property 
'    •-- to identify the window where you want to change the caption (Form1.hWnd), 
'    •-- then changes the text of that caption to "Welcome to VB."
    
'    •-- Remember that Visual Basic cannot verify that you are passing correct values 
'    •-- to a DLL procedure. If you pass incorrect values, the procedure may fail, which 
'    •-- may cause your Visual Basic application to hang... or worse. :)