OSBREAD

OSBREAD command reads data from a file starting at a specified byte location for a certain length of bytes, and assigns the data to a variable.

COMMAND SYNTAX

    OSBREAD var FROM file.var [ AT byte.expr ] LENGTH length.expr  \
            [ ON ERROR statements ]

OSBREAD performs an operating system block read on a UNIX or Windows file.

SYNTAX ELEMENTS

var specifies a variable to which the data read is assigned.

FROM file.var specifies a file from which the data is read.

AT byte.expr specifies a location inside the file from where the data reading operation is to start. If byte.expr is 0, the read begins at the beginning of the file.

LENGTH length.expr specifies length of data to be read from the file, starting at byte.expr. length.expr cannot be longer than the maximum string length determined by your system configuration.

ON ERROR statements are statements executed if a fatal error occurs (if the file is not open, or if the file is a read-only file). If you do not specify the ON ERROR clause, the program will terminate under such fatal error conditions.

STATUS Function Return Values After you execute OSBREAD, the STATUS function returns either 0 or a failure code.

NOTE

Before you use OSBREAD, you must open the file by using the OSOPEN or OPENSEQ command.

jBASE uses the ASCII 0 character [CHAR (0)] as a string-end delimiter. Therefore, ASCII 0 cannot be used in any string variable within jBASE. OSBREAD converts CHAR(0) to CHAR(128) when reading a block of data.

EXAMPLE

In the following example, the program test.b reads itself and outputs its contents to the screen: 

       OSOPEN 'test.b' TO MYFILE ELSE STOP
       OSBREAD Data FROM MYFILE AT 0 LENGTH 10000
       CRT Data

TAFJ note: if we use a variable for LENGTH, routine won't even compile: 

    expecting "LENGTH", found 'max_len' Probably due to unclosed Block.
    Please verify that all 'IF' has a 'END'

TAFJ R23 note: if the last CRLF is missing in a file, last data byte is truncated:

File test.txt (no CRLF in "Line 3"): 

    Line 1
    Line 2
    Line 3

Test routine: 

       OSOPEN 'test.txt' TO f_in ELSE
           CRT 'Open error'
           STOP
       END
       *
       OSBREAD data FROM f_in AT 0 LENGTH 100000 ON ERROR
           ret_stat = STATUS()
           CRT 'Read error (status = ' : DQUOTE(ret_stat) : ')'
           STOP
       END
       *
       OSCLOSE f_in
       CRT DQUOTE(data)
       STOP
       END

Output - TAFC: 

    "Line 1
    Line 2
    Line 3"

Output - TAFJ: 

    "Line 1
    Line 2
    Line "
Last update: Tue, 30 Jan 2024 09:14