Call C++ DLL from VBA - problem with string and LPCSTR*

[renatoab]

Hi,

I'm having problems when I try to call a function in a C++ DLL from VBA.

There's a function "execute" in a dll. I don't have the dll code, but I have a C++ function "run_execute" that calls that function "execute", and I'm trying to do the same on a VBA code.

I'm not sure what's going wrong but there's something about string arguments.

There are arguments of type char*, that I pass as String, Byval. It seems to be working, because the error occurs after reading files that I pass this way as string.

But there are arguments of type LPCSTR*, which I use to pass arrays of string, that I don't know how to deal with. I saw some examples, that seemed to work in a simple way, like simply using string, or using pointer to string, declaring an array of type LongPtr.

Does anyone know what I'm doing wrong, and how can I make it work? Is there anything about string length? Is there anything about usign system directory for dll?

Thank you.

Here's some sample of what I'm doing

' I'm using here LongPtr, but I also tried String
' I'm running this code on Office 2010 32 bits

Public Declare Function runTR Lib "C:\myfolder\mydll.dll" _
    Alias "_execute@48" _
    (ByVal flag1 As Long, _
    ByVal flag2 As Long, _
    ByVal flag3 As Long, _
    ByVal namefile1 As String, _
    ByVal namefile2 As String, _
    ByRef pointer_descritorEntrada() As LongPtr, _
    ByRef pointer_descritorSaida() As LongPtr, _
    ByRef valorEntrada() As Double, _
    ByRef valorSaida() As Double) As Long

sub run

    ' I'm skiping the long and double declarations, to show only the main problem

    Dim namefile1 As String
    Dim namefile2 As String

    namefile1 = "C:\myfolder\Example.plx"
    namefile2 = "C:\myfolder\Example.cfg"

    Dim dEntrada(1) As String
    Dim dSaida(0) As String

    dEntrada(0) = "Instruction_1"
    dEntrada(1) = "Instruction_2"
    dSaida(0) = "Result_tag_1"   

    Dim pointer_dEntrada(1) As LongPtr
    Dim pointer_dSaida(0) As LongPtr

    pointer_dEntrada(0) = StrPtr(dEntrada(0))
    pointer_dEntrada(1) = StrPtr(dEntrada(1))
    pointer_dSaida(0) = StrPtr(dSaida(0))

    dim error_index as Long

    error_index = runTR(flag1, _
                               flag2, _
                               flag3, _
                               namefile1, _
                               namefile2, _
                               pointer_dEntrada, _
                               pointer_dSaida, _
                               valorEntrada, _
                               valorSaida)
end sub

 

[John_w]

See if How To Pass a String Between Visual Basic and Your C DLL helps, specifically the DisplayStringByRef C function and the VB/VBA declaration and call.

 

[renatoab]

See if How To Pass a String Between Visual Basic and Your C DLL helps, specifically the DisplayStringByRef C function and the VB/VBA declaration and call.

I'd seen this example before. I tried this way, but it didn't work in my case.
This example is a little bit different: (1) the example has a string, I have an array if strings (2) I use VBA while the example uses VB.
I'm not sure if this makes any difference, but didn't work for me.

Thank you

 

[renatoab]

Problem when passing LPCSTR* to dll -> trying to debug -> problem when trying to write text file

I'm trying to debug to see what happens inside the dll, to fix the problem. I'm writing a text file in the dll (using fopen c++ command) to print the values but I'm having problem with it.

When I run the dll from other sources, the txt is generated with no problem. But when I run from VBA, an error occurs, and Excel closes.
I know the problem is with the text file, because without it the dll runs (with wrong results because my difficult with LPCSTR). I don't think there is any problem with directories, because the xlsm, dll and txt are in the same directory, in which I have writing permission, and is included in the environment variable PATH. I tried absolute and relative references, but the same occurs.

Do someone know anything different about writing text files from a dll called from VBA?