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Sharing Data with Memory Mapped Files

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2.94/5 (19 votes)
14 Nov 2010CPOL 98K   2.4K   26   5
How to use memory mapped files.

Screenshot - img1.gif

Screenshot - img2.gif

Introduction

This article shows how two processes can share data with each other with the help of memory mapped files. The example was written using VC++ 6.0

Background

I wanted a flexible way to share data in between two different processes. Memory mapped files have very important role in Windows, as well as in some other operating systems.

Using the code

In this sample application, one process will write some data to a memory mapped file and other processes will then read that data. Here I am using two different instances of the same application to both read from and write data to a memory mapped file.

Creating the memory mapped file and mapping it to memory

m_hFileMMF = CreateFileMapping(INVALID_HANDLE_VALUE,NULL,PAGE_READWRITE,0,4*1024,"MyMMF");
DWORD dwError = GetLastError();
if ( ! m_hFileMMF )
 { MessageBox(_T("Creation of file mapping failed"));
 }
 else
 { m_pViewMMFFile = MapViewOfFile(m_hFileMMF,FILE_MAP_ALL_ACCESS,0,0,0); // map all file
    if(! m_pViewMMFFile )
    { MessageBox(_T("MapViewOfFile function failed"));
    }
 }

Writing data to memory mapped file

UpdateData(TRUE);
g_mutex.Lock();
if(m_pViewMMFFile )
  lstrcpy( (LPTSTR) m_pViewMMFFile, m_Text);
g_mutex.Unlock();

Reading data from memory mapped file

g_mutex.Lock();
if(m_pViewMMFFile)
{
  lstrcpy(sReadText, (LPCTSTR) m_pViewMMFFile);
  m_ReadText = sReadText;
  GetDlgItem(IDC_EDIT2)->SetWindowText(m_ReadText);
}
g_mutex.Unlock();

Points of Interest

I think memory mapped files can solve many problems very easily but people don't use them very often.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

 
GeneralMy vote of 2 Pin
XTAL25610-Jan-12 18:52
XTAL25610-Jan-12 18:52 
QuestionHow the... Pin
Dave Kreskowiak14-Nov-10 17:59
mveDave Kreskowiak14-Nov-10 17:59 
GeneralCheck this too.. Pin
Sreekanth Muralidharan24-Jun-08 1:17
Sreekanth Muralidharan24-Jun-08 1:17 
GeneralA little simplistic Pin
Stuart Dootson16-Apr-07 21:33
professionalStuart Dootson16-Apr-07 21:33 
GeneralRe: A little simplistic Pin
Blake Miller17-Apr-07 7:52
Blake Miller17-Apr-07 7:52 

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