How to check whether a file is open already in COBOL?

I am trying to find out a way 开发者_开发技巧to check whether a file is already opened in COBOL, so that I can open it if it is closed or close it if it is opened.

Thnx.

Check the FILE STATUS and act accordingly.

Try the following:

Add a FILE-STATUS under the FILE-CONTROL, for example:

    FILE-CONTROL.
        SELECT  MYFILE ASSIGN MYDD
                ORGANIZATION SEQUENTIAL
                ACCESS       SEQUENTIAL
                FILE STATUS  MYFILE-STATUS.

Declare a FILE STATUS variable in WORKING-STORAGE as a PIC X(2) value, for example:

           01 MYFILE-STATUS   PIC X(2).
              88 MYFILE-ALREADY-OPEN   VALUE '41'.

Then in the PROCEDURE DIVISIONissue an OPEN for your file. Immediately following that, test the value of FILE STATUS as in:

    OPEN MYFILE....
    IF MYFILE-ALRADY-OPEN
       CLOSE MYFILE...
    END-IF
    IF MYFILE-STATUS <> '00'
       perform some sort of general error routine
    END-IF

Values of FILE STATUS where the first character is not a '9', are COBOL standard values so testing for '41' to detect an already open file should work on all COBOL implementations. Beware when the first character is a '9', these are vendor specific file status codes. Check out the following link for a good introduction to using COBOL FILE STATUS: http://www.simotime.com/vsmfsk01.htm

Your compiler may also provide a external API, such as CBL_CHECK_FILE_EXIST which can be found on Micro Focus COBOL, AcuCOBOL and Fujutsu COBOL.

For example, on Micro Focus COBOL:

 copy "cblproto.cpy".

 program-id. MYMAIN.
 working-storage section.
 01  .
     05  file-details    cblt-fileexist-buf.

 procedure division.
     call 'CBL_CHECK_FILE_EXIST' using 'mymain.cbl '
                                       file-details
     if  return-code not = 0
       display "File mymain.cbl does not exist (or error)"
     else
       display "File mymain.cbl size is " cblt-fe-filesize
       of file-details
     end-if
 end program MYMAIN.