New in version 6.3.0: See the new features.

Rewinding a sequential file to the beginning¶

frewind

Rewind a sequential file to the beginning


SYNTAX

frewind file_handle [err = label] [traps = label]

Rewinds the sequential file open specified in the file_handle.

If the file is open in read mode, the next sequential file read or write command operates at the beginning of the file.

file_handle

It can be the handle returned by the fopen command (it returns a negative number to differentitate the #channel case) or an integer in the range 1-64 specifying the number of the channel on which the sequential file, socket or pipe (opened by the open # command) is open. It may be a constant, field name or expression.

[err = label]

Errors return the trappable condition err, which may be trapped by the err = clause or by the general traps = clause. The error number is stored in the system variable sys.Error , and control passes to the line indicated by label. The error numbers are defined by manifest constants in the file errors.h, which is located in the Sculptor include directory. This file may be included in a program by means of an !include declaration. The possible errors are:

No

Manifest constant

Meaning

1

BAD_CHANNEL

file_handle is wrong

13

CHECK_ERRNO

general error, check errno

If an error occurs and is not trapped, an error message is displayed and control passes to the active menu, if any. If no menu is active the program exits.

[traps = label]

General purpose trap clause that traps any condition not explicitly trapped, passing control to the line indicated by label. It has the lowest priority, and is only invoked if a trappable condition has not been more explicitly trapped.


NOTES

  • If the handle/channel is already closed the command is ignored.


EXAMPLE

Use the frewind command to modify a previously written value:

!temp fHandle,,i2
!record fileHeader {
  magic,,i4
  description,,a64
}

fopen fHandle "binary_file_name" "w+"

fileHeader.magic = 0x1234
fileHeader.description = "File description"
fwrite fHandle fileHeader

. Rewind and modify the fileHeader magic number in the file
frewind fHandle
fileHeader.magic = 0x1235
fwrite fHandle fileHeader

RELATED TOPICS

tell()

fopen

fclose

fseek

rewind #

seek #

wind #

Sequential files

Fcmds

Traps