Language Reference

BACKSPACE

Purpose

The BACKSPACE statement positions an external file, connected for sequential access, before the preceding record.

Format

>>-BACKSPACE--+-u-------------------+--------------------------><
              '-(--position_list--)-'
 
 

u

is an external unit identifier. The value of u must not be an asterisk or a Hollerith constant.

position_list

is a list that must contain one unit specifier ([UNIT=]u) and can also contain one of each of the other valid specifiers:

[UNIT=] u

is a unit specifier in which u must be an external unit identifier whose value is not an asterisk. An external unit identifier refers to an external file that is represented by a scalar integer expression, whose value is in the range 1 through 2147483647. If the optional characters UNIT= are omitted, u must be the first item in position_list.

IOSTAT= ios

is an input/output status specifier that specifies the status of the input/output operation. ios is a scalar variable of type INTEGER(4) or default integer. When the BACKSPACE statement finishes executing, ios is defined with:

• A zero value if no error condition occurs
• A positive value if an error occurs.

ERR= stmt_label

is an error specifier that specifies the statement label of an executable statement in the same scoping unit to which control is to transfer in the case of an error. Coding the ERR= specifier suppresses error messages.

Rules

If there is no preceding record, the file position does not change. If the preceding record is the endfile record, the file is positioned before the endfile record. You cannot backspace over records that were written using list-directed or namelist formatting.

If the ERR= and IOSTAT= specifiers are set and an error is encountered, transfer is made to the statement specified by the ERR= specifier and a positive integer value is assigned to ios.

+-------------------------------IBM Extension--------------------------------+

If IOSTAT= and ERR= are not specified,

• The program stops if a severe error is encountered.
• The program continues to the next statement if a recoverable error is encountered and the ERR_RECOVERY run-time option is set to YES. If the option is set to NO, the program stops.

+----------------------------End of IBM Extension----------------------------+

Examples

   BACKSPACE 15
   BACKSPACE (UNIT=15,ERR=99)
      
  ·
  ·
  ·

99 PRINT *, "Unable to backspace file."
   END

Related Information

• Conditions and IOSTAT Values
• Chapter 8, Input/Output Concepts
• "Setting Runtime Options for Input/Output" in the User's Guide