Reading Data from Files, 3 of 9

Reading Files

While reading from a file, you can format the data from each field individually, and use DML functions to process the information before assigning it to a workspace object. Reading a file generally involves the following steps.

Open the file you want to read.
Read data from the file one record or line at a time.
Process the data and assign it to one or more workspace objects.
Close the file.

The FILEREAD and FILEVIEW commands have the same attributes and can do the same processing on your data. However, they differ in important ways:

The FILEREAD command loops automatically over all records in the file and processes them automatically. Use FILEREAD when all records in the file are the same.
The FILEVIEW command processes one record at a time. Use FILEVIEW when there is more than one type of record in the file.

Creating a Program to Read Data

The following table shows, for each method, the commands you need to open and close the input file, to read the file, and to handle errors that might occur.

Program Section	FILEREAD	FILEVIEW
Initialization	VARIABLE funit INTEGER TRAP ON error	VARIABLE funit INTEGER TRAP ON error
Body	funit = FILEOPEN(- 'alias/datafile' READ) FILEREAD funit . . . FILECLOSE funit	funit = FILEOPEN(- 'alias/datafile' READ) WHILE FILENEXT(funit) DO FILEVIEW funit . . . DOEND FILECLOSE funit
Normal Exit	RETURN	RETURN
Abnormal Exit	error: IF funit NE na THEN FILECLOSE funit	error: IF funit NE na THEN FILECLOSE funit

Note:

The error handling in the abnormal exit section of the programs closes the file only when the file is open. The FILEOPEN function signals an error when for any reason the system cannot open the file. The program tries to close the file after the ERROR label only when FUNIT holds a valid file unit number. You can add additional commands to the error handling section as well. These sections of the program are the same for both methods.