Positions file at preceding record.
Syntax
The syntax of the BACKSPACE
statement can take one of two forms:
Short form:
BACKSPACE integer-expression |
Long form:
BACKSPACE ( io-specifier-list ) |
- integer-expression
is the number of the unit connected to a sequential
file.
- io-specifier-list
is a list of the following comma-separated I/O
specifiers:
- [UNIT=]
unit
specifies the unit connected to an external file
opened for sequential access. unit must
be an integer expression that evaluates to a number greater than
0. If the optional keyword UNIT=is omitted, unit must be
the first item in io-specifier-list.
- ERR=stmt-label
specifies the label of an executable statement to
which control passes if an error occurs during statement execution.
- IOSTAT=integer-variable
returns the I/O status after the statement
executes. If the statement executes successfully, integer-variable
is set to zero. If an error occurs, it is set to a positive integer
that indicates which error occurred.
Description
The BACKSPACE
statement causes the external file connected to unit
to be positioned just before the preceding record of the file. The
file must be connected for sequential access.
Examples
The following statement causes the file connected to unit
10 to be positioned just before the preceding record:
The following statement causes the file connected to unit
17 to be positioned just before the preceding record. If an error
occurs during the execution of the statement, control passes to
the statement at label 99, and the error code is returned in ios:
BACKSPACE (17, ERR=99, IOSTAT=ios) |
Related statements
ENDFILE,
OPEN, and REWIND
Related concepts
For information about I/O concepts, see Chapter 8 “I/O and file handling”, which lists example
programs that use I/O. For information about I/O
formatting, see Chapter 11 “Intrinsic procedures”.
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