What is the Role of the Message Map in MFC?

The message map in MFC is a mechanism that maps Windows messages to specific handler functions within an application. It helps organize the code by directing messages (such as button clicks, key presses, or mouse movements) to the corresponding functions.

In MFC, message maps are declared using the BEGIN_MESSAGE_MAP and END_MESSAGE_MAP macros. Each message type is linked to a handler using specific macros, such as ON_COMMAND for commands or ON_WM_PAINT for paint events.

BEGIN_MESSAGE_MAP(CMyWindow, CWnd)
    ON_COMMAND(ID_HELP_ABOUT, &CMyWindow::OnHelpAbout)
    ON_WM_SIZE()
END_MESSAGE_MAP()

void CMyWindow::OnHelpAbout()
{
    // Display About dialog
}

void CMyWindow::OnSize(UINT nType, int cx, int cy)
{
    // Handle window resizing
}

Here, the OnHelpAbout function is linked to the “Help -> About” command, and OnSize is linked to the window resize message.

Message maps simplify handling different user inputs and system events in an organized and maintainable way.