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How to Use Streams

  • Article

You can use streams to transfer data into or out of a rich edit control. A stream is defined by an EDITSTREAM structure, which specifies a buffer and an application-defined callback function.

To read data into a rich edit control (that is, stream in the data), use the EM_STREAMIN message. The control repeatedly calls the application's callback function, which transfers a portion of the data into the buffer each time.

To save the contents of a rich edit control (that is, stream out the data), you can use the EM_STREAMOUT message. The control repeatedly writes to the buffer and then calls the application's callback function. For each call, the callback function saves the contents of the buffer.

What you need to know

Technologies

Prerequisites

  • C/C++
  • Windows User Interface Programming

Instructions

Use a Stream

The following code example shows how to read an .rtf file into a rich edit control. The file handle is passed to the callback function through the dwCookie member of the EDITSTREAM structure.

DWORD CALLBACK EditStreamCallback(DWORD_PTR dwCookie, 
                                  LPBYTE lpBuff,
                                  LONG cb, 
                                  PLONG pcb)
{
    HANDLE hFile = (HANDLE)dwCookie;
    
    if (ReadFile(hFile, lpBuff, cb, (DWORD *)pcb, NULL)) 
    {
        return 0;
    }
    
    return -1;
}

BOOL FillRichEditFromFile(HWND hwnd, LPCTSTR pszFile)
{
    BOOL fSuccess = FALSE;
    
    HANDLE hFile = CreateFile(pszFile, GENERIC_READ, 
                              FILE_SHARE_READ, 0, OPEN_EXISTING,
                              FILE_FLAG_SEQUENTIAL_SCAN, NULL);
        
    if (hFile != INVALID_HANDLE_VALUE) 
    {
        EDITSTREAM es = { 0 };
        
        es.pfnCallback = EditStreamCallback;
        es.dwCookie    = (DWORD_PTR)hFile;
        
        if (SendMessage(hwnd, EM_STREAMIN, SF_RTF, (LPARAM)&es) && es.dwError == 0) 
        {
                fSuccess = TRUE;
        }
        
        CloseHandle(hFile);
    }
    
    return fSuccess;
    
}

Using Rich Edit Controls

Windows common controls demo (CppWindowsCommonControls)