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How to do CreateFileMapping in a C++ DLL and access it in C#, VB and C++

, 10 Mar 2009
This is yet another example for memory mapped files. What is cool though is unlike other samples, I have a SetData(TCHAR* Key, TCHAR* value) / GetData(TCHAR* key) pattern here.
MMF_SetData_GetData.zip
tubelite
bin
Client_CSharp.exe
Client_CSharp.vshost.exe
Client_CSharp.vshost.exe.manifest
Client_VBNET.exe
Client_Win32Console.exe
Client_Win32Console.ilk
SHAREDMEM.dll
SHAREDMEM.exp
SHAREDMEM.ilk
SHAREDMEM.lib
CSharpConsumer
bin
Debug
WindowsFormsApplication1.exe
Properties
Settings.settings
SHAREDMEM
module.def
Release
mt.dep
sharedmem.dll.intermediate.manifest
sharedmem.pch
vc90.idb
sharedmem.vcproj.Pranav-PC.Pranav.user
UnmanagedConsumer
Release
mt.dep
Test1.exe.intermediate.manifest
vc90.idb
Test1.vcproj.Pranav-PC.Pranav.user
VBNETConsumer
bin
My Project
Application.myapp
Settings.settings
// sharedmem.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"
#include "sharedmem.h"
#include "tchar.h"
#include "stdio.h"

extern HANDLE m_hFileMMF, m_pViewMMFFile, hMutex;

class CMutex
{

public:
	CMutex()
	{
		if(!hMutex){
			hMutex = CreateMutex(
				NULL,              // default security attributes
				FALSE,             // initially not owned
				L"Global\\MMFMutex");             // unnamed mutex
		}

		WaitForSingleObject(  hMutex, INFINITE);  

	}

	~CMutex()
	{
		ReleaseMutex(hMutex);
	}

};

void SetRecordCount(int value)
{
	TCHAR* record = (TCHAR*)m_pViewMMFFile;
	swprintf_s(record, MAX_PATH, L"RECCNT=%d#", value);
}

extern "C" int GetRecordCount()
{
	TCHAR* record = (TCHAR*)m_pViewMMFFile;
	TCHAR temp[MAX_PATH];

	int recordCount = -1;

	TCHAR seps[]   = L"=#";
	TCHAR *token1 = NULL;
	TCHAR *next_token1 = NULL;

	_tcscpy_s(temp, MAX_PATH, record);

	token1 = _tcstok_s ( temp, seps, &next_token1);

	if(token1 && _tcscmp(token1, _T("RECCNT")) == 0)
	{
		token1 = _tcstok_s ( NULL, seps, &next_token1);

		recordCount = _ttoi(token1);
	}else
	{
		recordCount = 1;
		SetRecordCount(1);
	}

	return recordCount;
}


int nRecordCount = -1;

void RemoveValue(TCHAR* key)
{
	TCHAR* record = (TCHAR*)m_pViewMMFFile;

	TCHAR temp[MAX_PATH];

	nRecordCount = GetRecordCount();

	record+=MAX_PATH;

	//Try to look. If found, break out of for loop
	//Compact the memory immediately immediately
	//If you get time, strongly advice you to do a lazy compaction
	bool isRecordFound = false;
	int i;
	for(i= 1; i< nRecordCount; i++,record+=MAX_PATH)
	{
		TCHAR seps[]   = L"=#";
		TCHAR *token1 = NULL;
		TCHAR *next_token1 = NULL;

		_tcscpy_s(temp, MAX_PATH, record);

		token1 = _tcstok_s ( temp, seps, &next_token1);


		if(_tcscmp(token1, key) == 0)
		{
			isRecordFound = true;
			break;
		}
	}

	//start moving the records 
	for(; i< nRecordCount-1; i++, record+=MAX_PATH)
	{
		TCHAR* nextRecord = record + MAX_PATH;
		_tcscpy_s(record, MAX_PATH, nextRecord);
	}
}



TCHAR* IfExists(TCHAR* key, TCHAR** value = NULL)
{
	TCHAR* record = (TCHAR*)m_pViewMMFFile;

	TCHAR temp[MAX_PATH];

	nRecordCount = GetRecordCount();

	record+=MAX_PATH;
	for(int i=1; i< nRecordCount; i++,record+=MAX_PATH)
	{
		TCHAR seps[]   = L"=#";
		TCHAR *token1 = NULL;
		TCHAR *next_token1 = NULL;

		_tcscpy_s(temp, MAX_PATH, record);

		token1 = _tcstok_s ( temp, seps, &next_token1);

		if(_tcscmp(token1, key) == 0)
		{
			token1 = _tcstok_s ( NULL, seps, &next_token1);

			//return a copy of the value
			if(value!=NULL)
			{
				int len = _tcslen(token1)+1;
				*value = new TCHAR(len);
				_tcscpy_s(*value, len, token1);
			}

			return record;
		}
	}

	return NULL;
}

extern "C" TCHAR* GetValue(TCHAR* key)
{
	TCHAR* sRetVal = new TCHAR[MAX_PATH];

	CMutex mutex;	

	TCHAR* data = NULL;

	if(m_pViewMMFFile)
	{
		IfExists(key, &data);
	}

	return data;
}


extern "C" void SetValue(TCHAR* key, TCHAR* value)
{
	CMutex mutex;	

	if(m_pViewMMFFile )
	{
		if(value == NULL)
		{
			RemoveValue(key);
		}
		else
		{
			TCHAR* data = IfExists(key);
			if(data == NULL)
			{
				data = new TCHAR[MAX_PATH];
				swprintf_s(data, MAX_PATH, L"%s=%s#", key, value);

				//Add to end of the MMF
				TCHAR* record = (TCHAR*)m_pViewMMFFile;
				record += MAX_PATH*nRecordCount;
				nRecordCount++;

				SetRecordCount(nRecordCount);

				_tcscpy_s(record, MAX_PATH, data);
				delete data;
			}
			else
			{
				//Replace existing
				swprintf_s(data, MAX_PATH, L"%s=%s#", key, value);
			}
		}
	}
}

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About the Author

nkrscorpio
Software Developer
United States United States
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