OPEN statement
Remarks#
The COBOL OPEN statement initiates file processing. File resources in COBOL are defined in the ENVIRONMENT DIVISION, named in FD (File Descriptor) paragraphs. These fd names are used to access physical disk files and various options are specified in a SELECT clauses in the FILE-CONTROL paragraph of the INPUT-OUTPUT SECTION. A programmer is expected to test a FILE STATUS identifier for status and error codes.
Modes include INPUT, OUTPUT, I-O and EXTEND.
OPEN sample, with LINAGE mini report
COBOL *****************************************************************
* Example of LINAGE File Descriptor
* Tectonics: $ cocb -x linage.cob
* $ ./linage <filename ["linage.cob"]>
* $ cat -n mini-report
*****************************************************************
IDENTIFICATION DIVISION.
PROGRAM-ID. linage-demo.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
select optional data-file assign to file-name
organization is line sequential
file status is data-file-status.
select mini-report assign to "mini-report".
DATA DIVISION.
FILE SECTION.
FD data-file.
01 data-record.
88 endofdata value high-values.
02 data-line pic x(80).
FD mini-report
linage is 16 lines
with footing at 15
lines at top 2
lines at bottom 2.
01 report-line pic x(80).
WORKING-STORAGE SECTION.
01 command-arguments pic x(1024).
01 file-name pic x(160).
01 data-file-status pic 99.
01 lc pic 99.
01 report-line-blank.
02 filler pic x(18) value all "*".
02 filler pic x(05) value spaces.
02 filler pic x(34)
VALUE "THIS PAGE INTENTIONALLY LEFT BLANK".
02 filler pic x(05) value spaces.
02 filler pic x(18) value all "*".
01 report-line-data.
02 body-tag pic 9(6).
02 line-3 pic x(74).
01 report-line-header.
02 filler pic x(6) VALUE "PAGE: ".
02 page-no pic 9999.
02 filler pic x(24).
02 filler pic x(5) VALUE " LC: ".
02 header-tag pic 9(6).
02 filler pic x(23).
02 filler pic x(6) VALUE "DATE: ".
02 page-date pic x(6).
01 page-count pic 9999.
PROCEDURE DIVISION.
accept command-arguments from command-line end-accept.
string
command-arguments delimited by space
into file-name
end-string.
if file-name equal spaces
move "linage.cob" to file-name
end-if.
open input data-file.
read data-file
at end
display "File: " function trim(file-name) " open error"
go to early-exit
end-read.
open output mini-report.
write report-line
from report-line-blank
end-write.
move 1 to page-count.
accept page-date from date end-accept.
move page-count to page-no.
write report-line
from report-line-header
after advancing page
end-write.
perform readwrite-loop until endofdata.
display
"Normal termination, file name: "
function trim(file-name)
" ending status: "
data-file-status
close mini-report.
* Goto considered harmful? Bah! :)
early-exit.
close data-file.
exit program.
stop run.
****************************************************************
readwrite-loop.
move data-record to report-line-data
move linage-counter to body-tag
write report-line from report-line-data
end-of-page
add 1 to page-count end-add
move page-count to page-no
move linage-counter to header-tag
write report-line from report-line-header
after advancing page
end-write
end-write
read data-file
at end set endofdata to true
end-read
.
*****************************************************************
* Commentary
* LINAGE is set at a 20 line logical page
* 16 body lines
* 2 top lines
* A footer line at 15 (inside the body count)
* 2 bottom lines
* Build with:
* $ cobc -x -Wall -Wtruncate linage.cob
* Evaluate with:
* $ ./linage
* This will read in linage.cob and produce a useless mini-report
* $ cat -n mini-report
*****************************************************************
END PROGRAM linage-demo.