FSEEKO(3) Linux Programmer's Manual FSEEKO(3)
fseeko, ftello - seek to or report file position
int fseeko(FILE *stream, off_t offset, int whence);
off_t ftello(FILE *stream);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_FILE_OFFSET_BITS == 64 || _POSIX_C_SOURCE >= 200112L
(defining the obsolete _LARGEFILE_SOURCE macro also works)
The fseeko() and ftello() functions are identical to fseek(3) and ftell(3) (see fseek(3)), respectively, except that the offset argument of
fseeko() and the return value of ftello() is of type off_t instead of long.
On some architectures, both off_t and long are 32-bit types, but defining _FILE_OFFSET_BITS with the value 64 (before including any header
files) will turn off_t into a 64-bit type.
On successful completion, fseeko() returns 0, while ftello() returns the current offset. Otherwise, -1 is returned and errno is set to
indicate the error.
See the ERRORS in fseek(3).
These functions are available under glibc since version 2.1.
For an explanation of the terms used in this section, see attributes(7).
|Interface | Attribute | Value |
|fseeko(), ftello() | Thread safety | MT-Safe |
POSIX.1-2001, POSIX.1-2008, SUSv2.
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Check Out this Related Man Page
FSEEK(3) BSD Library Functions Manual FSEEK(3)
fgetpos, fseek, fseeko, fsetpos, ftell, ftello, rewind -- reposition a stream
Standard C Library (libc, -lc)
fseek(FILE *stream, long int offset, int whence);
fseeko(FILE *stream, off_t offset, int whence);
fgetpos(FILE * restrict stream, fpos_t * restrict pos);
fsetpos(FILE * restrict stream, const fpos_t * restrict pos);
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 the fseek() function except that the offset argument is of type off_t.
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 the ftell() function except that the 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
(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared (see clearerr(3)).
In this implementations, an ``fpos_t'' object is a complex object that represents both the position and the parse state of the stream making
these routines are the only way to portably reposition a text stream. The pos argument of fsetpos() must always be initialized by a call to
The rewind() function returns no value. Upon successful completion, fgetpos(), fseek(), fseeko(), and fsetpos() return 0. The functions
ftell() and ftello() return the current offset. Otherwise, fseek(), fseeko(), ftell(), and ftello() return -1 while fgetpos() and fsetpos()
return a nonzero value. On error all functions the global variable errno is set to indicate the error. Since the rewind() function does not
return an error code, applications need to clear errno before calling it in order to detect errors.
[EBADF] The stream specified is not a seekable stream.
[EINVAL] The whence argument to fseek() was not SEEK_SET, SEEK_END, or SEEK_CUR.
[EOVERFLOW] For ftell(), the current file offset cannot be represented correctly in an object of type long.
The function fgetpos(), fseek(), fseeko(), fsetpos(), ftell(), ftello(), and rewind() may also fail and set errno for any of the errors spec-
ified for the routines fflush(3), fstat(2), lseek(2), and malloc(3).
The fgetpos(), fsetpos(), fseek(), ftell(), and rewind() functions conform to ANSI X3.159-1989 (``ANSI C89''). The fseeko() and ftello()
functions conform to X/Open System Interfaces and Headers Issue 5 (``XSH5'').
The fgetpos() and fsetpos() functions don't store/set shift states of the stream in this implementation.
January 21, 2012 BSD