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Accessing Files |
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PxPlus includes an option called Direct File Access, which eliminates the need for programmers to explicitly OPEN/CLOSE files. (as of PxPlus v9.00)
This allows programmers to specify the path name of the file they want to access (as opposed to its channel number) on an IO command directive or function. The system will automatically open the file (if not already open) and use the channel on which it was opened.
Examples:
The following example shows using the READ directive to access the contents of the file "arcust" by key. The WRITE, REMOVE, EXTRACT, UPDATE, LOCK, UNLOCK and PURGE directives can also be used.
READ ("arcust",key="000555")
dump
! ERR=0, CTL=0, RET=2
! **********************************************************
! Level=1
! PGN="<Unsaved>"
AMT_OWING=11.43
ADDR1$="8450 Buga-Buga Drive"
CITY$="Unionville"
CUST_NO$="000555"
NAME$="Mike was here"
SALESPERSON$="WL"
The system file IO functions, such as the FIN function shown below, can use file names as well.
PRINT FIN("dealers","KEY_DEFINITION")
["Primary":1:1:30:"C"],["ByCompany":17:1:8],["ByName":3:1:30]+[4:1:30]
When opening the file, the system will apply the standard Prefix rules as applied on an OPEN. The value of HFN (highest unopened file number) will be used to determine the file number. The system variable LFO will be set to the file number used if a file is required.
The file will remain open until specifically closed using CLOSE ("..."), CLOSE (file_number), or a BEGIN is issued. The file will be left open after the directive so that subsequent IOs to the same file will use the same opened channel. This will allow a Read Next to process the file as long there are no intervening IO requests to the same file name.
The maximum number of concurrent files that will be opened dynamically is controlled by the F+ system parameter. By default, this parameter is set to 50, which limits the number of concurrent opens to 50. If this limit is reached, the oldest file accessed will automatically be closed by the system.
When a file is open (as a result of direct reference) and it contains an embedded data dictionary, the dictionary will be applied to the channel (i.e. the OPEN will be done as if IOL=* was specified).
Should the directive/function that is accessing the file have a REC= clause, it will not be applied to the OPEN. Dynamic OPENs will not be tied to an object but rather are accessible to the complete session.
When accessing the same file, care should be taken to ensure that the file names match. The system uses the exact spelling of the file names to determine if the file is already open.
Case sensitivity is applied based on the operating system: