A-Shell Reference

OPEN #channel, filespec, mode, recnovar, fstatvar {,end'file} {, wait'record} {,wait'file} {,read'only}

Opens the file. (Note that while internally there may be multiple physical files, from BASIC, the combination of the data file and index is treated as a single file. Unlike old ISAM, there is no need or possibility of opening up additional index files.)

Also note that unlike the OPEN statements for random and ISAM files, there is no record size parameter. The actual data record size on disk is one byte larger (due to a control byte) than the logical record size specified in the file index. There is also no span'blocks parameter, because it is effectively always on—i.e. the records are contiguous without regard to disk block size.

ch  (Num)  [in]

an integer expression (>0) specifying the file channel which will be needed for subsequent I/O operations on the file.

fspec  (String)  [in]

string expression containing file specification, in native or AMOS syntax. May contain embedded %env% variables, e.g. "%temp%\myfile.dat".  If no directory information is included, the search path consists of the current directory, followed by the [p,0] directory.

In ISAM-A, the specification is of a primary or secondary index (IDX) file. In the case of a primary index, the associated data (DAT) file will also be opened at the same time and accessed via the same channel. To reduce confusion, the file extension (IDX) is normally omitted, since the operation will open both the IDX and DAT files.

mode (literal keyword)  [in]

must be one of the following:

 

Although the OPEN for ISAM-A syntax differs somewhat from the OPEN for ISAM syntax, there is enough overlap that they can be confused if the INDEXED or INDEXED'EXCLUSIVE mode is specified without the ISAM' (or ISAMP' for ISAM-A) prefix. In the absences of the disambiguating prefix, the compiler will assume ISAM if the /I switch is specified, else it will assume ISAM-A.

recnovar  (F6)  [in]

holds the current record number. Normally, you never need to do anything explicitly with this variable since all operations are based on the index, but it will be set to the data record number after each successful index operation and is used as input by some record-level operations such as UPDATE'RECORD.

This variable must be F,6. It gets linked by address to the file's entry in the open file table, and thus must remain in scope for the duration of the open file channel. If this is not possible, for example, across function or SBX calls, you can manually reassign it to another variable using MX_FLSET. Or, to eliminate this limitation entirely, use XOPEN instead of OPEN.Also see the .RECNO(channel) dot function.

fstatvar (F6)  [in]

set to indicate the status of most operations, from the following table:

 

The same limitations apply here as to recnovar above. Also see the .FSTAT(channel) dot function.

The remaining parameters are all optional modifiers and may be specified in any order:

 

See Also