Question

Clarion dll gives a "Attempted to read or write protected memory" error

Asked by: rveede

Hi,
I've a .DLL file that's made with Clarion. This DLL file does some things and returns a string value.
I want to use some methods of this DLL in my C# program. So I used dllimport with the methods I want to use.
So far so good, but sometimes I get a "Attempted to read or write protected memory" error. Not all the time.

I am not sure if I'm using the DLL import right in this case.
This is my dllimport syntax:
[DllImport("C:\\callcw.dll", EntryPoint = "getKlantbyID")]
public static extern string getKlantbyID(string companyid, string klantid);

and this is the way i call this method:
string xmlPath = getKlantbyID(companyid, klantnummer).ToString();
companyid and klantnummer are both of the type 'string'.

This is the function prototype in Clarion:
getKlantbyID(Long, Long),String,Pascal
The variable it returns is of the type 'CString(500)'

I'm not sure but I think the error has to do with the way I'm using the DLL in C#.

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Asked On
2007-07-19 at 05:58:04ID22706757
Tags

protected

,

read

,

write

,

memory

,

attempted

,

Clarion

Topics

Databases Miscellaneous

,

C# Programming Language

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Answers

 

by: TheLearnedOnePosted on 2007-07-19 at 06:36:28ID: 19521711

The declaration has Long, Long, and you have string, string:

[DllImport("C:\\callcw.dll", EntryPoint = "getKlantbyID")]
public static extern string getKlantbyID(int companyid, int klantid);

Bob

 

by: rveedePosted on 2007-07-19 at 06:46:38ID: 19521812

It has to be that way else it wont work at all. In clarion I read the address to get the string value.
If I change the prototype to 'getKlantbyID(String, String),String,Pascal' it does not work.

 

by: TheLearnedOnePosted on 2007-07-19 at 06:51:01ID: 19521849

I wasn't talking about changing the Clarion prototype, I was talking about the C# p/invoke signature.

Bob

 

by: rveedePosted on 2007-07-19 at 06:53:49ID: 19521868

I understand, but I need to pass strings to the method, no int's.

It is working this way but i just get this "Attempted to read or write protected memory" randomly.

 

by: TheLearnedOnePosted on 2007-07-19 at 06:59:09ID: 19521920

That is a buffer overrun, and so it is not working correctly.  I don't understand how you can define Long values in the Clarion prototype, and use strings on the C# side.  Did you try changing the C# signature to use 'int'?

Bob

 

by: rveedePosted on 2007-07-19 at 07:06:59ID: 19521998

Take a look at this: http://attryde.com/clarion/cw_vb.htm
Especially the 'Passing String Parameters' section at the bottom.
There you will see a VB declaration of P/Invoke using a string and a clarion prototype with a long.

I can try to change the C# signature to use 'int' but how am I going to pass a string to it that way?

 

by: TheLearnedOnePosted on 2007-07-19 at 07:47:55ID: 19522435

That article describes the process for VB6, and C# doesn't marshal data the same way as VB6.

Bob

 

by: rveedePosted on 2007-07-20 at 00:40:25ID: 19529310

Does someone knows how to get this working?

 

by: TheLearnedOnePosted on 2007-07-20 at 07:25:16ID: 19531269

While I understand the C# side, I don't understand how Clarion marshals data.

Bob

 

by: rveedePosted on 2007-07-22 at 23:49:58ID: 19545446

If I let the Clarion DLL return the address of the variable, how can i read the Cstring on that address in C#?

I can use de address() function in Clarion to return the address as a Long.
The address value than looks like '230565520' for example.

 

by: TheLearnedOnePosted on 2007-07-23 at 06:24:58ID: 19547098

I am not sure that C# can handle CString, but I know that C++ can.  I have seen others write a C++.NET managed wrapper that you could use in C#.

Bob

 

by: rveedePosted on 2007-07-23 at 06:55:09ID: 19547382

I've found a solution.
I'm now using 'Marshal.PtrToStringAnsi(new IntPtr(getKlantbyID(companyID, klantID)))' to get the string value.
No more random "Attempted to read or write protected memory" error's for now.

 

by: TheLearnedOnePosted on 2007-07-23 at 07:23:51ID: 19547648

Cool, good job!!! b-)

Bob

 

by: Computer101Posted on 2007-10-21 at 18:10:21ID: 20119913

PAQed with points refunded (500)

Computer101
EE Admin

20120131-EE-VQP-002

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