C语言ftell()函数

Posted 2022-08-12 Dontla

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FSEEK(3)                                                             Linux Programmer's Manual                                                            FSEEK(3)

NAME
       fgetpos, fseek, fsetpos, ftell, rewind - reposition a stream

SYNOPSIS
       #include <stdio.h>

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

       long ftell(FILE *stream);

       void rewind(FILE *stream);

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

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 off‐
       set 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 ftell() function obtains the current value of the file position indicator for the stream pointed to by stream.

       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 non-UNIX 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 VALUE
       The rewind() function returns no value.  Upon successful completion, fgetpos(), fseek(), fsetpos() return 0, and ftell() returns the current offset.   Oth‐
       erwise, -1 is returned and errno is set to indicate the error.

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.  Or: the resulting file offset would be negative.

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

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────┬───────────────┬─────────┐
       │Interface                   │ Attribute     │ Value   │
       ├────────────────────────────┼───────────────┼─────────┤
       │fseek(), ftell(), rewind(), │ Thread safety │ MT-Safe │
       │fgetpos(), fsetpos()        │               │         │
       └────────────────────────────┴───────────────┴─────────┘

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, C89, C99.

SEE ALSO
       lseek(2), fseeko(3)

COLOPHON
       This page is part of release 4.04 of the Linux man-pages project.  A description o