XOPEN for ISAM-A
Updated July 2021
XOPEN #ch, fspec$, mode, recsiz {, flags}
This is equivalent to the traditional OPEN statement for ISAM files, except:
| • | OPEN eliminates the implicit connection between the fstatvar and recnovar variables normally specified in the OPEN, and the file access statements. The recnovar and fstatvar parameters are eliminated. |
| • | XOPEN allows for the various flags (WAIT'RECORD, WAIT'FILE, END'FILE,...) which must normally be specified as literals to the compiler to instead be evaluated at runtime. |
Parameters
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]
specifies the file access mode, and must be one of the following (case insensitive) compiler keywords:
Open Mode |
Meaning |
|---|---|
ISAMP' |
Same as INDEXED but forces operation to be interpreted as an ISAM-A open rather than an ISAM open, regardless of the COMPIL mode. Otherwise the COMPIL mode will determine whether to assume old ISAM or ISAM-A. |
ISAMP'INDEXED' |
Same as INDEXED'EXCLUSIVE but forces operation to be interpreted as an ISAM-A open rather than an ISAM open, regardless of the COMPIL mode. |
INDEXED |
Normal shared open. If file is already open by another user exclusively, job will wait (if the wait'record option specified) or receive ASB error 37 (file in use). See comment below this table. |
INDEXED' |
Open for exclusive use. If file is already open by another user in any mode, job will wait (if the wait'record option specified) or receive ASB error 37 (file in use). |
flags (B,4 or numeric expression) [in]
flags optionally specifies zero or more of the following modifiers:
Symbol |
Value |
Modifiers* |
|---|---|---|
FDVF_EXCLUSIVE |
&h0800 |
Convert INDEXED to INDEXED'EXCLUSIVE |
FDVF_READONLY |
&h1000 |
READ'ONLY |
FDVF_END_FILE |
&h2000 |
END'FILE |
FDVF_W_RECORD |
&h4000 |
WAIT'RECORD |
FDVF_W_FILE |
&h8000 |
WAIT'FILE |
Definition file: ashinc:addsfdv.def |
||
* These are the literal file OPEN modifiers that can be tacked on to the end of an ISAM-A OPEN statement.
Example
This example illustrates a generic Open function for ISAM-A files. Note that the mode parameter is hard-coded as ISAMP'INDEXED, but the flags parameter allows the possibility of upgrading that to exclusive (via the FDVF_EXCLUSIVE flag). This function checks if the file channel is already open and does nothing if it is, assuming that the specified channel matches the fspec).
Function Fn'Open'ISAMA(ch as b2:inputonly, fspec$ as s260:inputonly, recsiz as b2:inputonly, flags as b4:inputonly) as i4
if ch # 0 then ! if a non-zero channel specified
if eof(ch) = -1 then ! and it's not already open
xopen #ch, fspec$, ISAMP'INDEXED, recsiz, flags
endif
endif
.fn = ch
EndFunction
A typical call might look like...
if Fn'Open'ISAMA(ch=1234, fspec$="MYFILE", recsiz=128, flags= FDVF_EXCLUSIVE+FDVF_W'FILE) > 0 then
get #ch, isam'key(0) = mykey$, myrec
See Also
History
2020 June, A-Shell 6.5.1683: Statement added to A-Shell
