Issue Passing string from C# to C++ dll method and manipulating it.

[Peeyush81]

Hi,
I have created a win32 dll with an exported method.

extern "C" __declspec(dllexport) void LocateAddress(struct stLocateAddressParam arrAddressParam,int nClientType, LPTSTR outptr);

In this method i try to copy some value to the lpstr

strcpy(outptr,ptrTemp);

When I call this method from C++, it works fine. But when I try to call it from
C# using this syntax

[DllImport("xxx.dll", SetLastError = false)]
public static extern void LocateAddress(stLocateAddressParam locatAddressParam, int nClientType,StringBuilder s);

StringBuilder s = new StringBuilder(256);
LocateAddress(stLctAddrParam, 1, s);

the dll crashes at the point of copy( I found after debugging). I do pass other variables like a struct
but they are only input parameters and work well. If I comment the copy line
it works fine. I need to pass the output in a string to C#. From what I know,
it can be done either returning a string or passing a buffer as indicated at

http://msdn2.microsoft.com/en-us/library/s9ts558h.aspx

Am I missing something?

Thanks,
Peeyush

[radcaesar]

Here u go..

http://www.csharphelp.com/archives/archive63.html

[Peeyush81]

Here u go..

http://www.csharphelp.com/archives/archive63.html

That link doesent work .

But I investigated further in the meanwhile and checked that
the problem was when my C++ method signature contains both a struct
and an LPSTR ( pass by value and pass by reference??)

If
-I change the method to LocateAddress(struct stLocateAddressParam arrAddressParam,int nClientType);

- make Global variable in the dll class to store the LPSTR
- make another getsomething method to get this stored value
immediately after method call and call it, there is no crash.

I missed the crash message earlier , it says attempt to read or write protected memory. memory is corrupt.

Thanks,
Peeyush

[Peeyush81]

trying again the link worked. :-)