Delphi calling unmanaged dll works fine, but C# doesn't

3
votes

I've seen some topics about my issue, but they weren't so clear to help me.

My problem is: I have a Delphi 7 Application that calls an external dll, from a third-part (wich I have no access to source). I'm trying to convert the Delphi code to C# (.NET 2.0).

Here is the delphi code to call the dll:

function C500pchar(Comando : pchar):Integer; stdcall; external 'c50032.dll' name 'C500';

Here is my C# code to call the same dll:

[DllImport("C50032.DLL", CallingConvention = CallingConvention.StdCall, EntryPoint = "C500")]
    static extern int C500pchar(StringBuilder Comando);

This C# code is working fine when I run it from Visual Studio 2005, but when I try to run the exe file, it crashes when the application calls the Method C500pchar. I tried to copy all files from Release and Debug folders and even run the exe from the folders, but it just work when I'm running from VS.

Am I doing anything wrong?

EDIT: I'm working on Windows 7 and facing this issue. But I've tried running on Windows XP SP3 and worked fine.

1
c#delphidllunmanageddllimport
Is StringBuilder really the right type? Are you sure you don't want a regular String? (And does your DLL accept wide or narrow strings? I don't know Delphi well enough to read that from the signature.) - Rup
can you show the code that calls the function - David Heffernan
Please please can you show the code that calls the functions. - David Heffernan
private int c500(ref StringBuilder Comando) { int result = C500pchar(Comando); return result; } - Renan Vasconcelos
I would like to see the code that creates the StringBuilder. Also, what does the Delphi code do? How do you know how big a buffer to allocate in the StringBuilder? What does the C500pchar actually do? Presumably it copies text to the buffer passed to it. How much text? What is the return value. Seeing the Delphi code that calls the DLL would also help hugely. If I could see both the Delphi code to call the DLL and the full C# calling code then I'm sure I can find the error. Please do this as an edit to the question. - David Heffernan

1 Answers

3
votes

Your project runs in 32bit mode in visual studio, but in 64 bits mode when run directly. You must change the project settings so it runs in x86 instead of any cpu.