Clarion Community Help

Database Drivers

Choosing the Right Database Driver

Common Database Driver Features

Driver Strings

Clipper:Specifications

Clipper:Data Types

Clipper:Supported Commands and Attributes

Clipper:Driver Strings

Clipper:Other

Clipper:Specifications

The Clipper file driver is compatible with Clipper Summer '87 and Clipper 5.0. The default data file extension is *.DBF.

Keys and Indexes exist as separate files from the data file. Keys are dynamic–they automatically update as the data file changes. Indexes are static–they do not automatically update, but instead require the BUILD statement for updating. The default file extension for the index file is *.NTX.

The driver stores records as fixed length. It stores memo fields in a separate file. The memo file name takes the first eight characters of the File Label plus an extension of .DBT.

As a popular xBase database application development system, Clipper provides a common file format for many installed business applications and their data files. Use the Clipper driver to access these files in their native format.

Clipper:Data Types

The xBase file format stores all data as ASCII strings. You may either specify STRING types with declared pictures for each field, or specify native Clarion data types, which the driver converts automatically.

If your application reads and writes to existing files, a pictured STRING will suffice. However, if your application creates a Clipper file, you may require additional information for these Clipper types:

*       To create a Numeric field in the Data Dictionary, choose the REAL data type. In the External Name field on the Attributes tab, specify 'NumericFieldName=N(Precision,DecimalPlaces)' where NumericFieldName is the name of the field, Precision is the precision of the field and DecimalPlaces is the number of decimal places. With a REAL data type, you cannot access the Character or Places fields in the Field definition, you must specify those attributes with an expression in the External Name Field on the Attributes tab.

For example, if you want to create a field called Number with nine significant digits and two decimal places, enter 'Number=N(9,2) in the External Name field on the Attributes tab of the Field properties in the Data Dictionary.

If you're hand coding a native Clarion data type, add the NAME attribute using the same syntax.

If you're hand coding a STRING with picture, STRING(@N-_9.2), NAME('Number'), where Number is the field name.

*      To create a logical field, using the data dictionary, choose the BYTE data type. There are no special steps; however, see the miscellaneous section for tips on reading the data from the field.

If you're hand coding a STRING with picture, add the NAME attribute: STRING(1), NAME('LogFld = L').

*      To create a date field, using the data dictionary, choose the DATE data type, rather than LONG, which you usually use for the TopSpeed or Clarion file formats.

*      MEMO field declarations require the a pointer field in the file's record structure. Declare the pointer field as a STRING(10) or a LONG. This field will be stored in the .DBF file containing the offset of the memo in the .DBT file. The MEMO declaration must have a NAME() attribute naming the pointer field. An example file declaration follows:

File FILE, DRIVER('Clipper')

Memo1  MEMO(200),NAME('Notes')

Memo2  MEMO(200),NAME('Text')

Rec    RECORD

Mem1Ptr LONG,NAME('Notes')

Mem2Ptr STRING(10),NAME('Text')

      END

    END

Whenever possible, use the File Import Utility in the Dictionary Editor to define your files.

Clipper:File Specifications/Maximums

File Size:             2,000,000,000 bytes

Records per File:      1,000,000,000

Record Size:           4,000 bytes (Clipper '87)

                      8,192 bytes (Clipper 5.0)

Field Size

    Character:        254 bytes (Clipper '87)

                      2048 bytes (Clipper 5.0)

    Date:             8 bytes

    Logical:          1 byte

    Numeric:          20 bytes including decimal point

    Memo:             65,520 bytes (see note)

Field Name:            10 characters

Fields per Record:     1024

Keys/Indexes per File: No Limit

Key Sizes

    Character:        100 bytes

    Numeric, Date:    8 bytes

Memo fields per File:  Dependent on available memory

Open Files:            Operating system dependent