Reading and Writing Icons from ExtractIcon

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows, version 3.1

SUMMARY

This article is specifically about device dependent icons. The ExtractIcon() function does not save the contents of the icon to a file. The programmer needs to implement this in his or her application. Below are code samples that allow you to read and write the data to a file so that DrawIcon() can be used.

MORE INFORMATION

The following is a summary of the steps needed to save the hIcon to a file:

1. Get the desired handle to the icon by using ExtractIcon().

// -----------------------------------------------
//   Parameters: hIcon - passed in
//   Returns:    TRUE on success, FALSE on failure
// -----------------------------------------------
int NEAR _pascal SaveMyIcon( HICON hIcon)

  int       fh, i, iResult;
  UINT      uiSize;
  DWORD     dwSize;
  OFSTRUCT  of;

    if (!hIcon)
      return FALSE;

    dwSize  = GlobalSize(hIcon);
    lpGMem  = GlobalLock(hIcon);
    fh = OpenFile ("myicon.bin", &of, OF_WRITE | OF_CREATE);

    if (fh == -1)  // If NOT opened successfully.
    {
     MessageBox(NULL, "Unable to create file", NULL, MB_OK );
     return FALSE;
    }

    uiSize = _lwrite(fh, (LPSTR)lpGMem, (UINT)dwSize);
    _lclose(fh);

    if (uiSize == -1 || uiSize < (UINT)dwSize)
    {
       MessageBox(NULL, "Unable to read file", NULL, MB_OK );
       return FALSE;
    }
    else // Everything worked, return hGMem.
    {
      return (HICON)hGMem;
    }

The following is a summary of the steps needed to read the hIcon from a file:

1. Open the file with OpenFile.

// --------------------------------------
// Read in the binary icon data from disk
// --------------------------------------

  int       iResult, fh;
  UINT      nBytesRead;
  struct    _stat   buf;
  OFSTRUCT  ofFileInfo;

  nBytesRead = 0;
  if ( OpenFile((LPSTR)"myicon.bin",(LPOFSTRUCT)&ofFileInfo,OF_EXIST) != -1

  {
    // Open the file. Its existence has already been checked.
    fh = _lopen("myicon.bin", OF_READ);
    if (fh == -1)  // if NOT opened successfully
      return FALSE;

    // File the file structure to get the file size.
    iResult = _fstat(fh, &buf);
    if ( !iResult)
    {
      hGMem = GlobalAlloc(GHND, (DWORD)buf.st_size);
      if (0==hGMem)
      {
        _lclose(fh);
        return(FALSE);
      }

      // Lock the memory.
      if (!(lpGMem = GlobalLock(hGMem)))
      {
        GlobalFree(hGMem);
        _lclose(fh);
        return(FALSE);
      }

      // Seek to the beginning of the file.
      _llseek(fh, 0, 0);
      nBytesRead = _lread(fh, (LPSTR)lpGMem, buf.st_size );
    }
    _lclose(fh);

    if (nBytesRead == -1 || nBytesRead < buf.st_size)
    {
      MessageBox(NULL, "Unable to read file", NULL, MB_OK );
      return FALSE;
    }
    else // Everything worked, return hGMem.
    {
      return (HICON)hGMem;
    }
  }
  else
  {
    MessageBox( NULL, "File not found", NULL, MB_OK );
    return FALSE;
  }

WARNING: This will work correctly until the user changes his or her display-driver type to a different resolution, or from mono to color, or from color to mono.