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Top Forums Programming Incompatible data type fpos_t in C Post 302976358 by Corona688 on Tuesday 28th of June 2016 02:18:28 PM
Old 06-28-2016
From man fsetpos:

Code:
       The fgetpos() and fsetpos() functions are alternate interfaces  equivaâ
       lent  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 repoâ
       sition a text stream.

So you are playing with fire by assuming that fpos_t is an integer.

I recommend fseek instead:
Code:
void write_line(FILE *fp, int rec_no, line_rec *arec)
{
        long woffset = (rec_no - 1) * sizeof(line_rec);
        fseek(fp, woffset, SEEK_SET);
        fwrite(arec, sizeof(line_rec), 1, fp);
}

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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, 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 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 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 cur- rent offset. Otherwise, -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. 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). CONFORMING TO
C89, C99. SEE ALSO
lseek(2), fseeko(3) COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
1993-11-29 FSEEK(3)
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