Microsoft Windows Clipboard

Also Known As: CLP

Type Metafile

Colors Bilevel to 24-bit

Compression None

Maximum Image Size 32Kx32K and 2Gx2G pixels

Multiple Images Per File Yes

Numerical Format Little-endian

Originator Microsoft Corporation

Platform Microsoft Windows

Supporting Applications Microsoft Clipboard and ClipBook Viewer

See Also Microsoft Bitmap, Microsoft Metafile, DIF, SYLK, RTF

Usage
Used as a "one-format-saves-all" solution for easily storing data in Windows to disk.

Comments
A useful and under-utilized format. Programmers can safely assume that every installation of Windows will have the ability to read and write Clipboard files.

The Clipboard file format is used to store Microsoft Windows Clipboard data to disk. The Clipboard is an area of shared memory found in the Windows operating system, and is the simplest mechanism available to exchange data between applications running in the Windows environment.

Contents:
File Organization
File Details
For Further Information

A set of functions in the Windows API is used to transfer data between the Clipboard and Windows applications. For example, the Cut, Copy, Clear, Paste, and Undo functions found in many Windows applications all use these function to access Clipboard memory as an area for temporary storage and data exchange. However, only one Windows application may access the Clipboard at a time. The Clipboard can also be accessed directly using the built-in Windows applications Clipboard Viewer and ClipBook Viewer.

The Clipboard Viewer is a simple application used to view the entire contents of the Clipboard and to save its data to disk using the CLP file format. The ClipBook Viewer is an extended version of the Clipboard Viewer that allows stored data to be divided into separate pages of information and shared over a Microsoft (NetBEUI) network using the OLE or DDE protocols. Each page in the ClipBook may hold the data captured by a single Cut or Copy operation. ClipBook may contain a maximum of 127 separate pages, each identified by a name up to 47 characters in length, and limited in size only by the amount of available disk space. Each page of the ClipBook may be stored in a separate CLP file.

The Clipboard Viewer and ClipBook Viewer are separate programs, but both use the executable file name clipbrd.exe, so it is not likely you will find both programs installed in the same Windows environment.

The Clipboard Viewer under Windows 2.x and 3.x is found in the Main group box. Windows for Workgroups 3.x and Windows NT 3.x provide only the ClipBook Viewer, also found in the Main group box.

Clipboard Viewer is not installed by default in Windows 95. To install the Clipboard Viewer under Windows 95, you must select Add/Remove Programs in Control Panel, click the Windows Setup tab, click Accessories, and then click Details. Click the Clipboard Viewer check box to select it, and then click OK or Apply. The Clipboard Viewer will be installed and a shortcut will be placed in the Accessories menu under the Programs menu.

The CD-ROM version of Windows 95 and CD-ROM Extras for Microsoft Windows 95 Upgrade also includes the ClipBook Viewer, but the floppy disk version of Windows 95 does not. If you install Windows 95 over Windows for Workgroups version 3.1, and during Setup choose to not install the Windows 95 Clipboard Viewer, Windows 95 retains and will use the Windows for Workgroups ClipBook Viewer.

It is important to realize that both the Clipboard and ClipBook Viewer are only applications that access the Clipboard and its data, and are not the Clipboard themselves. This point is often a source of confusion for both Windows users and programmers alike.

File Organization

Clipboard files use a very simple data format, but can be quite complicated because they can store many types of data. The CLP file format begins with a header and is followed by a directory of one or more records that indicates the type and location of data within the Clipboard file. Following these records are the actual Clipboard data. (See Figure Microsoft Windows Clipboard-1.)

Figure Microsoft Windows Clipboard-1: Basic layout of a CLP file

[Graphic: Figure Microsoft Windows Clipboard-1]

There will be one section of data per record. The standard Clipboard data formats are listed in Table Microsoft Windows Clipboard-1.

Table Microsoft Windows Clipboard-1: Standard Clipboard Data Formats
Data Format Format ID Description

TEXT 0x0001 ANSI text

BITMAP 0x0002 Windows Device-Dependent Bitmap

METAFILE 0x0003 Windows Clipboard Metafile

SYLK 0x0004 Microsoft spreadsheet format

DIF 0x0005 Soft Arts spreadsheet format

TIFF 0x0006 Adobe Tag Image File Format

OEMTEXT 0x0007 ASCII text

DIB 0x0008 Windows Device-Independent Bitmap

PALETTE 0x0009 Windows DIB Color Palette

PENDATA 0x000A Microsoft Pen Windows data

RIFF 0x000B Microsoft Resource Interchange File Format

WAVE 0x000C Microsoft Audio File Format

UNICODETEXT 0x000D Unicode text (Windows NT only)

ENHMETAFILE 0x000E Windows Enhanced Metafile (Windows 95 and NT only)

HDROP 0x000F Double NULL-terminated list of strings (Windows 95 only)

LOCALE 0x0010 Language and character set specifier (Windows 95 only)

Table Microsoft Windows Clipboard-1: Standard Clipboard Data Formats
Data Format	Format ID	Description
TEXT	0x0001	ANSI text
BITMAP	0x0002	Windows Device-Dependent Bitmap
METAFILE	0x0003	Windows Clipboard Metafile
SYLK	0x0004	Microsoft spreadsheet format
DIF	0x0005	Soft Arts spreadsheet format
TIFF	0x0006	Adobe Tag Image File Format
OEMTEXT	0x0007	ASCII text
DIB	0x0008	Windows Device-Independent Bitmap
PALETTE	0x0009	Windows DIB Color Palette
PENDATA	0x000A	Microsoft Pen Windows data
RIFF	0x000B	Microsoft Resource Interchange File Format
WAVE	0x000C	Microsoft Audio File Format
UNICODETEXT	0x000D	Unicode text (Windows NT only)
ENHMETAFILE	0x000E	Windows Enhanced Metafile (Windows 95 and NT only)
HDROP	0x000F	Double NULL-terminated list of strings (Windows 95 only)
LOCALE	0x0010	Language and character set specifier (Windows 95 only)

Most of the native Windows data formats are supported by the Clipboard. The Clipboard is also capable of storing private or user-defined data formats (Table Microsoft Windows Metafile-2). Applications such as the Microsoft Windows Write word processor store a variety of private data formats using the Clipboard. You can also store any other file format as private data inside of a CLP file and read the file into the Clipboard using the Clipboard Viewer or your own Clipboard-aware application. Your application is then responsible for parsing and displaying the private data.

Table Microsoft Windows Clipboard-2: Private Clipboard Data Formats
Data Formats Format ID Description

OWNERDISPLAY 0x0080 Private data not displayable on the Clipboard

DSPTEXT 0x0081 Display Text

DSPBITMAP 0x0082 Display Bitmap

DSPMETAFILEPICT 0x0083 Display Metafile Picture

DSPENHMETAFILE 0x008E Display Enhanced Metafile

PRIVATEFIRST 0x0200 First Private Data Format

PRIVATELAST 0x02FF Last Private Data Format

GDIOBJFIRST 0x0300 First Private Graphics Device Interface Object

GDIOBJLAST 0x03FF Last Private Graphics Device Interface Object

Table Microsoft Windows Clipboard-2: Private Clipboard Data Formats
Data Formats	Format ID	Description
OWNERDISPLAY	0x0080	Private data not displayable on the Clipboard
DSPTEXT	0x0081	Display Text
DSPBITMAP	0x0082	Display Bitmap
DSPMETAFILEPICT	0x0083	Display Metafile Picture
DSPENHMETAFILE	0x008E	Display Enhanced Metafile
PRIVATEFIRST	0x0200	First Private Data Format
PRIVATELAST	0x02FF	Last Private Data Format
GDIOBJFIRST	0x0300	First Private Graphics Device Interface Object
GDIOBJLAST	0x03FF	Last Private Graphics Device Interface Object

When a CLP file is read by a Clipboard viewer, the data of the first usable entry will be displayed. It is therefore necessary to store the most important data first in a CLP file. For example, you might store the same piece of text in both the TEXT and OEMTEXT formats. Windows would use the TEXT data, and other applications that use only the ASCII character set would use the OEMTEXT data. The same text data could also be stored as RTF and UNICODETEXT in the same CLP file.

Not every flavor of Windows is capable of supporting every Clipboard data format. For example, ENHMETAFILE is not supported by Windows 3.x and UNICODETEXT is presently only supported by Windows NT. If Windows cannot find data in a usable format on the Clipboard, it will attempt to convert a recognized data format to one considered more suitable. For example, TEXT or OEMTEXT data may be converted to UNICODETEXT; METAFILEPICT to ENHMETAFILE; BITMAP to DIB, and DIB to PALETTE. Unrecognized formats are ignored and not displayed by the viewers.

File Details

The CLP header is four bytes in length and has the following format:

typedef struct _ClpHeader
{
    WORD FileId;        /* File identifier (always 3C50h) */
    WORD FormatCount;   /* Number of records in directory */
} CLPHEADER;

FileId is used to identify a CLP file. This value is always 3C50h.

FormatCount is the number of record entries in the format directory.

Clipboard Records

Following the header is one or more records that indicate the type and location of data within the Clipboard file. The number of records is specified by the FormatCount field in the header. Each record may be from 11 to 89 bytes in length and has the following format:

typedef struct _FormatRecord
{
    WORD  FormatId;       /* Format Identifier */
    DWORD DataLength;     /* Number of bytes in the data */
    DWORD DataOffset;     /* Offset of the data in the file */
    BYTE  FormatName[];   /* Format name */
} FORMATRECORD;

FormatId identifies the type of data indicated by this record. Valid values for this field are listed in the Format ID columns of Tables Microsoft Windows Clipboard-1 and Microsoft Windows Clipboard-2.

DataLength specifies the length of the data in bytes.

DataOffset indicates the offset of the data within the Clipboard file. The offset is always calculated from the beginning of the file.

FormatName is a plain-text string that describes the name of the format. This string will be "Text" for TEXT data, "Bitmap" for BITMAP data, and so forth. Private data types, such as "Rich Text Format", will also be described. This string may be up to 78 characters in length and is always terminated with a NULL (0x00).

The format of an entire Clipboard file can be defined as such:

typedef struct _ClipboardFormat
{
    CLPHEADER ClpHeader;
    FORMATRECORD ClpRecords[ClpHeader.FormatCount];
    BYTE Data[];
} CLIPBOARDFORMAT;

Clipboard Data

The CLP format supports a bewildering variety of data formats. Most of these formats are documented as separate file formats described elsewhere in this book. Following is a description of the format data types listed in Tables Microsoft Windows Clipboard-1 and Microsoft Windows Clipboard-2.

TEXT is one or more strings of 8-bit ANSI characters. Each string is terminated by a carriage return (0x0D) and a line feed (0x0A). A NULL (0x00) byte indicates the end of the TEXT data. The ANSI character set is the default character set used by Windows.

BITMAP is a Microsoft Device-Dependent Bitmap (DDB). Refer to the Microsoft Windows Bitmap format article for more information on the DDB format.

METAFILE is a standard Windows Metafile, but is preceded by an additional header used by the Clipboard. Refer to the Microsoft Windows Metafile format article for the format of the Clipboard Metafile.

SYLK is the Microsoft Symbolic Link data format used by Microsoft Excel, Chart, and Multiplan to store spreadsheet data. The SYLK data is stored as ASCII text with each line terminated with a carriage return and line feed. Refer to the Microsoft SYLK file format article for more information on the SYLK format.

DIF is the Software Arts Data Interchange Format used to store spreadsheet data. The DIF data is stored as ASCII text with each line terminated with a carriage return and line feed. Refer to the Lotus DIF file format article for more information on the DIF format.

TIFF is the Tag Image File Format created by Aldus, Hewlett-Packard, and others, and is now administered by Adobe Systems. Refer to the Tag Image File Format article for further information on TIFF.

OEMTEXT is one or more strings of 7-bit ASCII characters. Each string is terminated by a carriage return (0x0D) and a line feed (0x0A). A NULL (0x00) byte indicates the end of the OEMTEXT data. The ASCII character set is the default character set used by MS-DOS.

DIB is a Microsoft Device-Independent Bitmap (DIB). Refer to the Microsoft Windows Bitmap format article for more information on the DIB format.

PALETTE is a DIB color palette. Refer to the Microsoft Windows Bitmap format article for more information on the DIB color palettes.

RIFF is the Microsoft Resource Interchange File Format. This is Microsoft's "store anything" multimedia file format. Refer to the Microsoft RIFF article for more information.

WAVE is the Microsoft Waveform audio file format (.wav files). A wave file is nothing more than a RIFF file that stores only digital audio data.

UNICODETEXT is one or more strings of 16-bit Unicode characters. Each string is terminated by a carriage return (0x000D) and a line feed (0x000A). A NULL (0x0000) byte indicates the end of the UNICODETEXT data. The Unicode character set is the default character set used by Windows NT and Win32.

ENHMETAFILE is an Enhanced Windows Metafile found on Win32 systems. Refer to the Microsoft Windows Metafile format article for the format of the Enhanced Metafile.

OWNERDISPLAY is private data that is not recognized by the Clipboard, and is therefore not displayed by the Clipboard Viewer. The FormatName field of this data's record should yield a clue as to the format of the data.

DSPTEXT is a collection of private text. This data is stored using the same format as the TEXT format, and will be displayed as text, but is not available via the TEXT format ID.

DSPBITMAP is a collection of private text. This data is stored using the same format as the BITMAP format, and will be displayed as text, but is not retrievable using the BITMAP format ID.

DSPMETAFILEPICT is a collection of private text. This data is stored using the same format as the METAFILEPICT format, and will be displayed as text, but is not retrievable using the METAFILEPICT format ID.

DSPENHMETAFILE is a collection of private text. This data is stored using the same format as the ENHMETAFILE format, and will be displayed as text, but is not retrievable using the ENHMETAFILE format ID.

GDIOBJFIRST and GDIOBJLAST are a range of reserved values use to register private GDI objects. GDI objects include brushes, pens, palettes, and fonts. Under Windows the object is created first in memory and then saved to the Clipboard using the SetClipboardData() functions call. The handle of the GDI object and a value in the range of GDIOBJFIRST and GDIOBJLAST (inclusive) are passed to the function.

PRIVATEFIRST and PRIVATELAST are a range of reserved values used to register private data formats. There is no official registration of private data format numbers, so your reader application needs to both recognize this value and the FormatName string to properly identify the private data.

For example, let's say you want to import a 32K IFF file into your application through the Clipboard. You might construct a CLP file with a single record and containing the IFF file data:

typedef struct _PrivateIffFormat
{
    WORD  FileId;           /* 0x3C50 */
    WORD  FormatCount;      /* 0x0001 */
    WORD  FormatId;         /* 0x0200 */
    DWORD DataLength;       /* 0x00007FFF */
    DWORD DataOffset;       /* 0x00000026 */
    BYTE  FormatName[];     /* "Interchange File Format\0" */
    BYTE  Data[];           /* The entire IFF file */
} PRIVATEIFFFORMAT;

In this example we see a CLP file that contains a single record describing a private format with an ID value of 0x200. The data is 32K in size and begins 39 bytes into the file. Once this file has been read into the Clipboard the IFF file data may be read and parsed by any application that can access the Clipboard.

For Further Information

There is no official CLP file format specification. The Clipboard File Format and Clipboard management functions are described in detail in:

Microsoft Windows Programmer's Reference, Volumes 2 and 4, Microsoft Press, Redmond, WA, 1990.

The Microsoft Developers Network (MSDN) distributes several files containing information on the CLP format. These files may be found on the MSDN CD, or on the Microsoft Web site at:

http://www.microsoft.com/developr/MSDN/

Type	Metafile
Colors	Bilevel to 24-bit
Compression	None
Maximum Image Size	32Kx32K and 2Gx2G pixels
Multiple Images Per File	Yes
Numerical Format	Little-endian
Originator	Microsoft Corporation
Platform	Microsoft Windows
Supporting Applications	Microsoft Clipboard and ClipBook Viewer
See Also	Microsoft Bitmap, Microsoft Metafile, DIF, SYLK, RTF