FSEEK(3) | Library Functions Manual | FSEEK(3)

# NAME

`fgetpos`, `fseek`, `fseeko`, `fsetpos`, `ftell`, `ftello`, `rewind` — reposition a stream

# SYNOPSIS

`#include <stdio.h>`

int
`fgetpos`(FILE *stream, fpos_t *pos);

int
`fseek`(FILE *stream, long offset, int whence);

int
`fseeko`(FILE *stream, off_t offset, int whence);

int
`fsetpos`(FILE *stream, const fpos_t *pos);

long
`ftell`(FILE *stream);

off_t
`ftello`(FILE *stream);

void
`rewind`(FILE *stream);

# DESCRIPTION

The `fseek`() function sets the file position indicator for the stream pointed to by stream. The new position, measured in bytes, is obtained by adding offset bytes to the position specified by whence. If whence is set to `SEEK_SET`, `SEEK_CUR`, or `SEEK_END`, the offset is relative to the start of the file, the current position indicator, or end-of-file, respectively. A successful call to the `fseek`() function clears the end-of-file indicator for the stream and undoes any effects of the ungetc(3) function on the same stream.

The `fseeko`() function is identical to `fseek`() except that it takes an off_t as its offset.

The `ftell`() function obtains the current value of the file position indicator for the stream pointed to by stream.

The `ftello`() function is identical to `ftell`() except that its return value is of type off_t.

The `rewind`() function sets the file position indicator for the stream pointed to by stream to the beginning of the file. It is equivalent to:

`(void)fseek(stream, 0L, SEEK_SET)`

except that the error indicator for the stream is also cleared (see clearerr(3)).

The `fgetpos`() and `fsetpos`() functions are alternate interfaces equivalent to `ftell`() and `fseek`() (with whence set to `SEEK_SET`), setting and storing the current value of the file offset into or from the object referenced by pos. On some systems an “fpos_t” object may be a complex object and these routines may be the only way to portably reposition a text stream.

# RETURN VALUES

The `rewind`() function returns no value. Prefer `fseek`(), which is just as portable, and does not hide errors. Upon successful completion, `fgetpos`(), `fseek`(), `fseeko`(), and `fsetpos`() return 0 and `ftell`() and `ftello`() return the current offset. Otherwise, `fseek`(), `fseeko`(), `ftell`(), and `ftello`() return -1 and `fgetpos`() and `fsetpos`() return a non-zero value and the global variable errno is set to indicate the error.

# ERRORS

The `fgetpos`(), `fseek`(), `fseeko`(), `fsetpos`(), `ftell`(), `ftello`(), and `rewind`() functions will fail if:

[`EBADF`]
  The stream specified is not a seekable stream.

Additionally, the `fseek`() and `fseeko`() functions will fail if:

[`EINVAL`]
  The whence argument was not `SEEK_SET`, `SEEK_END`, or `SEEK_CUR`.

Additionally, the `ftell`() function will fail if:

[`EOVERFLOW`]
  The value of the file position indicator is too large to be represented by a long.

Finally, the functions `fgetpos`(), `fseek`(), `fseeko`(), `fsetpos`(), `ftell`(), and `ftello`() may also fail and set errno for any of the errors specified for the routines fflush(3), fstat(2), lseek(2), and malloc(3).

# SEE ALSO

lseek(2)

# STANDARDS

The `fgetpos`(), `fsetpos`(), `fseek`(), `ftell`(), and `rewind`() functions conform to ANSI X3.159-1989 (“ANSI C89”) and X/Open Portability Guide Issue 4 (“XPG4”).

The `fseeko`() and `ftello`() functions conform to X/Open Portability Guide Issue 4 (“XPG4”).

# HISTORY

The functions `fseek`(), `ftell`(), and `rewind`() first appeared in Version 7 AT&T UNIX.

September 11, 2022 | Debian