• OPEN statement establishes a connection between the logical file and its associated physical file.
• It opens the file for subsequent processing (e.g., reading, writing, updating).
• The program can't able to process a file without opening it.

Syntax -

OPEN opening-mode file-name.

Parameters -

• opening-mode - Specifies the file opening mode. Mode is mandatory with OPEN statement.
• file-name - Specifies 8-character logical file name defined inside the program. Multiple files can be opened with OPEN statement.

Opening Modes -

Mode	Description
INPUT	For reading operations only.
OUTPUT	For writing operations only. If a file already exists, ts contents overwritten.
I-O	For both reading and writing. Useful for updating files. The file should exist before to open in I-O mode.
EXTEND	For appending records to an existing file. It applies for sequential access files only.

Allowed file operations based on OPEN modes -

For Sequential Files -

	INPUT Mode	OUTPUT Mode	I-O Mode	EXTEND Mode
READ	X		X
WRITE		X		X
REWRITE			X

For Indexed and Relative Files -

	Operation	INPUT Mode	OUTPUT Mode	I-O Mode	EXTEND Mode
Sequential Access	READ	X		X
	WRITE		X		X
	REWRITE			X
	START	X		X
	DELETE			X
Random Access	READ	X		X
	WRITE		X	X
	REWRITE			X
	START
	DELETE			X
Dynamic Access	READ	X		X
	WRITE		X	X
	REWRITE			X
	START	X		X
	DELETE			X

Error Handling -

Let us assume the FILE STATUS clause is coded with a variable -

• If the file opened successfully, the file status code is updated as ZERO (0).
• If the file is not opened successfully, the file status code is updated with the error code.

The below table shows the possible file status codes when the OPEN statement failed -

File Opening mode	File Status if Unsuccessful
INPUT	Open is unsuccessful. (file status 35)
I-O	Open is unsuccessful. (file status 35)
OUTPUT	Open causes the file to be created.
EXTEND	Open is unsuccessful. (file status 35)
INPUT (optional file) I-O (optional file) EXTEND (optional file)	Open causes the file to be created. (file status 05)

Examples -

Scenario1 - Opening EMPFILE for reading.

 OPEN INPUT EMPFILE.

Scenario2 - Opening EMPFILE for writing.

 OPEN OUTPUT EMPFILE.

Scenario3 - Opening EMPFILE1, EMPFILE2 for reading.

 OPEN INPUT EMPFILE1
            EMPFILE2.

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