fvicent / VB6DynamicCall

Dynamic argument passing and function calls for VB6

VB6DynamicCall

Dynamic argument passing and function calls for VB6.

Rationale

Functions are not first-class citizens in VB6. All you have is the AddressOf keyword in order to get a pointer to a function (especially useful for interfacing with the Win32 API), but there is no simple way to call a function by address nor to figure out the arguments passed to that function at runtime. While an easy task in modern languages, a simple callback mechanism implementation in VB6 leads to boilerplate code and weird workarounds. VB6DynamicCall aims to overcome these limitations.

Usage

The CallByAddress() function lets you call a VB6 function by passing the result of AddressOf as an argument. If the target function requires certain arguments, you can "attach" them before making the call. For example, if this is our target function:

Public Sub AddIntegers(ByVal a As Integer, ByVal b As Integer)
    MsgBox CStr(a) & " + " & CStr(b) & " = " & CStr(a + b)
End Sub

We can invoke AddIntegers(7, 5) by doing:

Call AttachInteger(7)
Call AttachInteger(5)
Call CallByAddress(AddressOf AddIntegers)

Arguments are attached from left to right.

You will find out more examples and the API declarations in the test VB6 application under tests/VB6DynamicCallTest.