dBaseIII: Supported Commands and Attributes

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File Attributes

Supported

 

CREATE

Y

 

DRIVER(filetype [,driver string])

Y

 

NAME

Y

 

ENCRYPT

N

 

OWNER(password)

N

 

RECLAIM

N1

 

PRE(prefix)

Y

 

BINDABLE

Y

 

THREAD

Y12

 

EXTERNAL(member)

Y

 

DLL([flag])

Y

 

OEM

Y

 

 

File Structures

Supported

 

INDEX

Y

 

KEY

Y

 

MEMO

Y

 

BLOB

N

 

RECORD

Y

 

 

Index, Key, Memo Attributes

Supported

 

BINARY

N

 

DUP

Y2

 

NOCASE

Y

 

OPT

N

 

PRIMARY

Y

 

NAME

Y

 

Ascending Components

Y

 

Descending Components

Y

 

Mixed Components

N

 

 

Field Attributes

Supported

 

DIM

N

 

OVER

Y

 

NAME

Y

 

 

File Procedures

Supported

 

BOF(file)

Y8

 

BUFFER(file)

N

 

BUILD(file)

Y

 

BUILD(key)

Y

 

BUILD(index)

Y

 

BUILD(index, components)

Y3

 

BUILD(index, components, filter)

N

 

BYTES(file)

N

 

CLOSE(file)

Y

 

COPY(file, new file)

Y4

 

CREATE(file)

Y

 

DUPLICATE(file)

Y

 

DUPLICATE(key)

Y

 

EMPTY(file)

Y

 

EOF(file)

Y8

 

FLUSH(file)

Y

 

LOCK(file)

N

 

NAME(label)

Y

 

OPEN(file, access mode)

Y5

 

PACK(file)

Y

 

POINTER(file)

Y9

 

POINTER(key)

Y9

 

POSITION(file)

Y10

 

POSITION(key)

Y10

 

RECORDS(file)

Y11

 

RECORDS(key)

Y11

 

REMOVE(file)

Y

 

RENAME(file, new file)

Y4

 

SEND(file, message)

Y

 

SHARE(file, access mode)

Y5

 

STATUS(file)

Y

 

STREAM(file)

Y

 

UNLOCK(file)

N

 

 

Record Access

Supported

 

ADD(file)

Y6

 

ADD(file, length)

N

 

APPEND(file)

Y6

 

APPEND(file, length)

N

 

DELETE(file)

Y1

 

GET(file,key)

Y

 

GET(file, filepointer)

Y

 

GET(file, filepointer, length)

N

 

GET(key, keypointer)

Y

 

HOLD(file)

Y7

 

NEXT(file)

Y

 

NOMEMO(file)

Y

 

PREVIOUS(file)

Y

 

PUT(file)

Y

 

PUT(file, filepointer)

Y

 

PUT(file, filepointer, length)

N

 

RELEASE(file)

Y

 

REGET(file,string)

Y

 

REGET(key,string)

Y

 

RESET(file,string)

Y

 

RESET(key,string)

Y

 

SET(file)

Y

 

SET(file, key)

Y

 

SET(file, filepointer)

Y

 

SET(key)

Y

 

SET(key, key)

Y

 

SET(key, keypointer)

Y

 

SET(key, key, filepointer)

Y

 

SKIP(file, count)

Y

 

WATCH(file)

Y

 

 

Transaction Processing

Supported

 

LOGOUT(timeout, file, ..., file)

N

 

COMMIT

N

 

ROLLBACK

N

 

 

Null Data Processing

Supported

 

NULL(field)

N

 

SETNULL(field)

N

 

SETNULL(file,field)

N

 

SETNONNULL(field)

N

Notes

1      When the driver deletes a record from a dBase III database, the record is not physically removed, instead the driver marks it inactive. Memo fields are not physically removed from the memo file, however they cannot be retrieved if they refer to an inactive record. Key values are removed from the index files. To remove records and memo fields permanently, execute a PACK(file).

 

To those programmers familiar with dBase III, this driver processes deleted records consistent with the way dBase III processes them after the SET DELETED ON command is issued. Records marked for deletion are ignored from processing by executable code statements, but remain in the data file.

2      dBase III does not support any form of unique index. So the DUP attribute must be on all keys.

3      When building dynamic indexes, the components may take one of two forms:

  BUILD(DynNdx, '+Pre:FLD1, -Pre:FLD2')

This form specifies the names of the fields on which to build the index. The field names must appear as specified in the fields' NAME() attribute if supplied, or must be the label name. A prefix may be used for compatibility with Clarion conventions but is ignored.

  BUILD(DynNdx, 'T[Expression]')

This form specifies the type and Expression used to build an index--see Miscellaneous--Key Definition below.

4      These commands copy data and memo files using newfile, which may specify a new file name or directory. Key or index files are copied if the newfile is a subdirectory specification. To copy an index file to a new file, use a special form of the copy or rename command:

   COPY(file,'<index>|<newfile>')

This returns File Not Found if an invalid index is passed. The COPY command assumes a default extension of ".NDX" for both the source and the target file names if none is specified. If you require a file name without an extension, terminate the name with a period. Given the file structure:

Clar2  FILE,CREATE,DRIVER('dBase3'),PRE(CL2)

NumKey  KEY(+CL2:Num),DUP

StrKey  KEY(+CL2:Str1)

StrKey2 KEY(+CL2:Str2)

AMemo   MEMO(100), NAME('mem')

Record  RECORD

Num      STRING(@n-_9.2)

STR1     STRING(2)

STR2     STRING(2)

Mem      STRING(10)

       END

      END

The following commands copy this file definition to A:

COPY(Clar2,'A:\CLAR2')

COPY(Clar2,'StrKey|A:\STRKEY')

COPY(Clar2,'StrKey2|A:\STRKEY2')

COPY(Clar2,'NumKey|A:\NUMKEY')

After these calls, the following files would exist on drive A: CLAR2.DBF, CLAR2.DBT, STRKEY.NDX, STRKEY2.NDX, and NUMKEY.NDX.

5      You do not need SHARE (or VSHARE) in any environment (for example, Novell) that supplies file locking as part of the operating system.

6      The ADD statement tests for duplicate keys before modifying the data file or its associated KEY files. Consequently it is slower than APPEND which performs no checks and does not update KEYs. When adding large amounts of data to a database use APPEND...BUILD in preference to ADD.

7      dBase III performs record locking by locking the entire record within the data file. This prevents read access to other processes. Therefore we recommend minimizing the amount of time for which a record is held.

8      Although the driver supports these functions, we do not recommend their use. They must physically access the files and add overhead. Instead, test the value returned by ERRORCODE() after each sequential access. NEXT or PREVIOUS post Error 33 (Record Not Available) if an attempt is made to access a record beyond the end or beginning of the file.

9      There is no distinction between file pointers and key pointers; they both return the record number for any given record.

10     POSITION(file) returns a STRING(12). POSITION(key) returns a STRING the size of the key fields + 4 bytes.

11     Under dBase III, the RECORDS() function reports the same number of records for the data file and its keys and indexes. Usually there will be no difference in the number of records unless the INDEX is out of date. Because the DELETE statement does not physically remove records, the number of records reported by the RECORDS() function includes inactive records. Exercise care when using this function.

12     THREADed files consume additional file handles for each thread that accesses the file.