HP 3000 Manuals HP 3000 Manuals
BACKSPACE Statement (Executable) The BACKSPACE statement positions a sequential file or device at the preceding record.---------------------------------------------------------------------------------------------- | | | | | Item | Description/Default | Restrictions | | | | | ---------------------------------------------------------------------------------------------- | | | | | unit | Expression giving the unit | Must be a nonnegative | | | number of a connected file. | integer. | | | | | ---------------------------------------------------------------------------------------------- | | | | | variable_name | Error code return. | Must be an integer type. | | array_element | | | | scalar_record_field_name | | | | | | | ---------------------------------------------------------------------------------------------- | | | | | label | Statement label. | Must be an executable | | | | statement in the same | | | | program unit as the | | | | BACKSPACE statement. | | | | | ---------------------------------------------------------------------------------------------- Semantics If the prefix UNIT= is omitted and the unit specifier is present, unit must be the first item in the list. If the ERR specifier is present and an error occurs during execution of a BACKSPACE statement, control transfers to the statement specified by label rather than aborting the program. If the IOSTAT specifier is present and an error occurs, the error code is returned in the IOSTAT variable and the program is not aborted. Refer to Appendix A for IOSTAT error codes. If the file is positioned at its beginning, a BACKSPACE statement has no effect. As an extension to the ANSI 77 standard, BACKSPACE operations are allowed on files open for direct access. The file is positioned at the preceding record, provided it is not already at the beginning of the file. Examples Notes --------------------------------------------------------------------------------------- BACKSPACE 10 The sequential file connected to unit 10 is backspaced one record. BACKSPACE (UNIT=k+3,IOSTAT=j,ERR=100) The file connected to unit k+3 is backspaced one record. If an error occurs, control transfers to statement 100, and the error code is stored in variable j. If no error occurs, j is set to 0, and control transfers to the next statement. BACKSPACE (UNIT=k+3,IOSTAT=j) The file connected to unit k+3 is backspaced one record. If an error occurs, the error code is stored in the variable j. If no error occurs, j is set to 0. In both cases, control transfers to the next statement. BACKSPACE (UNIT=k+3,ERR=100) The file connected to unit k+3 is backspaced one record. If an error occurs, control transfers to statement 100. If no error occurs, control transfers to the next statement.
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