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CProcessData : A template class to ease up SendMessage calls across processes

, 9 Jun 2005
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CProcessData is a template class that makes it easy to use data allocated in a different process, and is useful when making inter-process SendMessage/PostMessage calls.

Overview

CProcessData is a template class that makes it easy to use data allocated in a different process, and is useful when making inter-process SendMessage/PostMessage calls.

Example Scenario - 1

Imagine that you are sending a DTM_SETSYSTEMTIME message to a Date/Time picker control in a different process.

Without CProcessData

SYSTEMTIME systim;
//Populate systim

HANDLE hProc = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pid);
LPVOID lpData = VirtualAllocEx(hProc, NULL, 
    sizeof SYSTEMTIME, MEM_COMMIT, PAGE_READWRITE);
WriteProcessMemory(hProc, lpData, (LPCVOID)&systim, 
    sizeof SYSTEMTIME, NULL);            

DWORD dwResult = (DWORD)::SendMessage(hwnd, 
    DTM_SETSYSTEMTIME, GDT_VALID, (LPARAM)&lpData);

if(dwResult == 0)
{
    DWORD err = GetLastError();
    //...
}

VirtualFreeEx(hProc, lpData, NULL, MEM_RELEASE);
CloseHandle(hProc);

Using CProcessData

SYSTEMTIME systim;
//Populate systim

CProcessData<SYSTEMTIME> data(pid);
data.WriteData(systim);

DWORD dwResult = (DWORD)::SendMessage(hwnd, 
    DTM_SETSYSTEMTIME, GDT_VALID, (LPARAM)data.GetData());
    
if(dwResult == 0)
{
    DWORD err = GetLastError();
    //...
}

Note only have you saved on lines of code, but you don't run the risk of forgetting to free the allocated memory or closing the process handle.

Example Scenario - 2

Imagine that you are retrieving toolbar info from a toolbar control in a different process.

Without CProcessData

HANDLE hProc = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pid);
LPVOID lpData = VirtualAllocEx(hProc, NULL, 
    sizeof TBBUTTON, MEM_COMMIT, PAGE_READWRITE);      

::SendMessage(hwnd, TB_GETBUTTON, index, (LPARAM)lpData);

TBBUTTON tb;
ReadProcessMemory(hProc, lpData,(LPVOID)&tb, 
    sizeof TBBUTTON, NULL)

CUSTOMDATA cus;
ReadProcessMemory(hProc, (LPCVOID)tb.dwData, (LPVOID)&cus, 
    sizeof CUSTOMDATA, NULL)

VirtualFreeEx(hProc,lpData,NULL,MEM_RELEASE);
CloseHandle(hProc);

Using CProcessData

CProcessData<TBBUTTON> data(pid);

::SendMessage(hwnd, TB_GETBUTTON, index, 
    (LPARAM)data.GetData());

TBBUTTON tb;
data.ReadData(&tb);    

CUSTOMDATA cus;
data.ReadData<CUSTOMDATA>(&cus,(LPCVOID)tb.dwData);

Pretty neat, huh?

Class Reference

Constructor

CProcessData(DWORD dwProcessId = 0, DWORD dwDesiredAccess = PROCESS_ALL_ACCESS, DWORD flAllocationType = MEM_COMMIT, DWORD flProtect = PAGE_READWRITE)

If you pass in a dwProcessId of 0, the current process Id is used. For the other arguments, see MSDN documentation for OpenProcess and VirtualAllocEx.

WriteData

BOOL WriteData(const T& data)

WriteData copies data to memory in the foreign process

ReadData

BOOL ReadData(T* data)

ReadData reads back from the memory in the foreign process into data.

ReadData (template version)

template<typename TSUBTYPE> BOOL ReadData(TSUBTYPE* data, LPCVOID lpData)

Templated ReadData that's used to read a specific data type from a memory address located in the foreign process.

Full source listing

[Listing has been formatted to fit within 600 pixels. Actual source code (included as a download) is formatted for wider screens]

/*
    Author  :    Nishant Sivakumar
    Date    :    June 9, 2005
    Info    :    Template class that makes it easy to use data allocated
                 in a different process. Useful when making inter-process
                 SendMessage/PostMessage calls.            
    Contact :    nish#voidnish.com
*/

//ProcessData.h

#pragma once

template<typename T> class CProcessData
{
public:    
    /*
        If you pass in a dwProcessId of 0, the current process Id is used.
        For the other arguments, see MSDN documentation for OpenProcess and
        VirtualAllocEx.
    */
    CProcessData(DWORD dwProcessId = 0, 
        DWORD dwDesiredAccess = PROCESS_ALL_ACCESS,
        DWORD flAllocationType = MEM_COMMIT, DWORD flProtect = PAGE_READWRITE)
    {
        m_hProcess = OpenProcess(dwDesiredAccess, FALSE, 
            dwProcessId ? dwProcessId : GetCurrentProcessId());
        ASSERT(m_hProcess);
        if(m_hProcess)
        {
            m_lpData = VirtualAllocEx(m_hProcess, NULL, sizeof T, 
                flAllocationType, flProtect);
            ASSERT(m_lpData);
        }
    }

    ~CProcessData()
    {
        if(m_hProcess)
        {            
            if(m_lpData)
            {
                VirtualFreeEx(m_hProcess, m_lpData, NULL, MEM_RELEASE);
            }
            CloseHandle(m_hProcess);
        }
    }

    //WriteData is used to copy data to memory in the foreign process
    BOOL WriteData(const T& data)
    {
        return (m_hProcess && m_lpData) ? WriteProcessMemory(
            m_hProcess, m_lpData, 
            (LPCVOID)&data, sizeof T, NULL) : FALSE;
    }

    //ReadData reads back data from memory in the foreign process
    BOOL ReadData(T* data)
    {
        return (m_hProcess && m_lpData) ? ReadProcessMemory(
            m_hProcess, m_lpData, 
            (LPVOID)data, sizeof T, NULL) : FALSE;
    }

    //Templated ReadData that's used to read a specific data type from
    //a memory address located in the foreign process
    template<typename TSUBTYPE> BOOL ReadData(
        TSUBTYPE* data, LPCVOID lpData)
    {
        return m_hProcess ? ReadProcessMemory(m_hProcess, lpData, 
            (LPVOID)data, sizeof TSUBTYPE, NULL) : FALSE;
    }

    //Gets the address of the allocated memory in the foreign process
    const T* GetData()
    {
        return (m_hProcess && m_lpData) ? (T*)m_lpData : NULL;
    }
private:
    T m_Data;
    HANDLE m_hProcess;
    LPVOID m_lpData;
};

History

  • June 16, 2005 : Small bug fix in destructor. (VirtualFreeEx and CloseHandle were in the wrong order)
  • June 10, 2005 : Article first published.
  • June 9, 2005 : Class written.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Nish Sivakumar

United States United States
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
 
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - www.voidnish.com where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff - blog.voidnish.com.
 
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket as well as a programming book – Extending MFC applications with the .NET Framework.
 
Nish's latest book C++/CLI in Action published by Manning Publications is now available for purchase. You can read more about the book on his blog.
 
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.

Comments and Discussions

 
Generaldtor order PinsussAnonymous15-Jun-05 4:06 
GeneralRe: dtor order and more PinsussAnonymous15-Jun-05 4:20 
GeneralRe: dtor order and more PinstaffNishant Sivakumar15-Jun-05 18:55 
GeneralRe: dtor order PinstaffNishant Sivakumar15-Jun-05 18:40 
GeneralNice work &amp;&amp; AnswerToQAboutExample PinmemberTom Archer12-Jun-05 1:05 
GeneralRe: Nice work &amp;&amp; AnswerToQAboutExample PinstaffNishant Sivakumar15-Jun-05 19:00 
GeneralOh my... PinmemberYoSilver11-Jun-05 13:49 
GeneralRe: Oh my... PinstaffNishant Sivakumar15-Jun-05 19:00 
GeneralGood Work PinmemberMichael A. Barnhart11-Jun-05 11:54 
GeneralRe: Good Work PinstaffNishant Sivakumar15-Jun-05 19:00 
GeneralLooks interesting, but... Pinmemberthe-unforgiven10-Jun-05 0:29 
GeneralRe: Looks interesting, but... PinstaffNishant Sivakumar10-Jun-05 0:37 
GeneralRe: Looks interesting, but... Pinmemberthe-unforgiven10-Jun-05 0:46 
GeneralRe: Looks interesting, but... PinmemberBugByter11-Jun-05 1:43 
GeneralRe: Looks interesting, but... PinmemberGary R. Wheeler11-Jun-05 1:44 

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