DOCERR: Corrections to Program Manager Group File Format Docs

The information in this article applies to:

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

SUMMARY

The text below provides additions and corrections to the documentation of the Microsoft Windows Program Manager group (.GRP) file format. This format is documented in Chapter 5 of the "Microsoft Windows Software Development Kit: Programmer's Reference, Volume 4: Resources" manual and in the associated online help files (WIN31WH.HLP and WIN31QH.HLP) provided with the Microsoft Windows Software Development Kit (SDK) version 3.1.

MORE INFORMATION

• In the "Organization of a Group File" section, page 61, the third paragraph is incorrect; it says:

        The item data entries are followed by entries that contain the
        color data for the application icons.
  

  Group files do not contain color data. The application icons use system colors only, and do not require any color data to be saved in the group file.

• The GROUPHEADER structure is incorrectly documented on page 62. The wBitsPerPixel and wPlanes fields are only one byte long. The correct GROUPHEADER structure is as follows:

        struct tagGROUPHEADER {
            char  cIdentifier[4];
            WORD  wCheckSum;
            WORD  cbGroup;
            WORD  nCmdShow;
            RECT  rcNormal;
            POINT ptMin;
            WORD  pName;
            WORD  wLogPixelsX;
            WORD  wLogPixelsY;
            BYTE  bBitsPerPixel;
            BYTE  bPlanes;
            WORD  wReserved;  // Should be 0x0000
            WORD  cItems;
            WORD  rgiItems[cItems];
        }
  
  

• The cbGroup field in the GROUPHEADER structure (described on page 62) specifies the size of the group file not including the tag data. This is in accord with Windows 3.0 group files, which do not contain any tag data. In Windows 3.1 group files, cbGroup can be used as an offset to the tag data.
• The description of the rgiItems field in the GROUPHEADER structure on page 63 is missing two words. The description should be:

        Specifies an array of offsets to ITEMDATA structures.
  

• Page 64 says that the pHeader field in the ITEMDATA structure points to the resource header for the icon, but fails to specify the structure of the resource header. Its structure is as follows:

        struct {
            int xHotSpot;    // Should be 0
            int yHotSpot;    // Should be 0
            int cx;          // Icon width
            int cy;          // Icon height
            int cbWidth;     // Bytes per row accounting
                             // for WORD alignment
            BYTE bPlanes;    // Count of planes
            BYTE bBitsPixel; // Bits per pixel
          }
  
  

• The last TAGDATA structure (described on page 64-65) in the group file will have 0xFFFF as the value for its wID. This simply signals the end of file.