Error message in VC++

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I am new for VC++.I am trying to change MFCDLL file for my Project.My Task is Multiple Port access.that means user accesses Multiple Port at same time.The below code is "Port On/Off" Function.
Old Code

C++

extern "C" __declspec(dllexport) void PortExit(int val)
{
	m_exitflag=val;
}
it is working on One - One Relationship that menas if i connect one COM Port .It is ok.But when i connect multiple port it is not worked.So i changed my code like this.
New Code
extern "C" __declspec(dllexport) void PortExit(int val,char *Ports)
{
	m_exitflag=val;
       port=Ports;
}

here,Port means get Port No.But it is not working.Why?I got this error message when i access this Dll in my Project .it is in C#.net

Message    : Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
Stack Trace:    at Testing.MultiplePrint.PortExit(Int32 ExitValue, String port)

Here MultiplePrint is Usercontrol .it develops in C#.net.
So Please Tell me.How to solve this issue .~~It is very urgent.~~

Posted 27-Jul-11 20:30pm

naraayanan

Updated 27-Jul-11 21:13pm

walterhevedeich

v4

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Philippe Mori · Answer 1 · 2011-07-28T16:15:00

Solution 2

Does your port variable is a null terminated string or a single char. If it is a single char, then on C# side, it should probably be a byte.

Posted 28-Jul-11 16:15pm

Philippe Mori

Updated 28-Jul-11 16:16pm

v2

Comments

naraayanan 29-Jul-11 0:03am

Thanks for reply.It is a String.So I used in my C#.net Project as a String.I set a value of Port number in this char *Ports in the PortExit.

Philippe Mori 29-Jul-11 7:50am

Then if it is a string.... you probably have to tell C# what kind on string is is. In that case, I think it is an ANSI string (single byte) and by default C# probably assume Unicode (two bytes).

naraayanan 31-Jul-11 23:34pm

Thanks Philippe

Debojyoti Majumder · Answer 2 · 2011-07-27T21:00:00

Solution 1

In your C# project declare the PortExit signature like this,

C#

PortExit(Int32 ExitValue, out string port)
{
....
}

I guess this will solve your problem.

Posted 27-Jul-11 21:00pm

Debojyoti Majumder

Comments

naraayanan 28-Jul-11 4:14am

Thanks for your reply .. But I got this error
Error 5 The best overloaded method match for 'Testing.MultiplePrint.SetExit(int, out string)' has some invalid arguments E:\Testing\Testing\Testing\Testing\MultiplePrint.cs 73 20 Testing
What will i do?

Richard MacCutchan 28-Jul-11 5:28am

Well the message is quite clear, your SetExit() call on line 73 is incorrect. If you really do not understand this message you should go back to your C# documentation at the section on overloaded methods.