toolchain/gcc/newlib/libc/unix/pwrite.c

   1 /*
   2 FUNCTION
   3 <<pwrite>>---write a file from specified position
   4
   5 INDEX
   6         pwrite
   7 INDEX
   8         _pwrite_r
   9
  10 ANSI_SYNOPSIS
  11         #include <unistd.h>
  12         ssize_t pwrite(int <[fd]>, const void *<[buf]>,
  13                        size_t <[n]>, off_t <[off]>);
  14         ssize_t _pwrite_r(struct _reent *<[rptr]>, int <[fd]>,
  15                           const void *<[buf]>, size_t <[n]>, off_t <[off]>);
  16
  17 TRAD_SYNOPSIS
  18         #include <unistd.h>
  19         ssize_t pwrite(<[fd]>, <[buf]>, <[n]>, <[off]>)
  20         int <[fd]>;
  21         const void *<[buf]>;
  22         size_t <[n]>;
  23         off_t <[off]>;
  24
  25         ssize_t _pwrite_r(<[rptr]>, <[fd]>, <[buf]>, <[n]>, <[off]>)
  26         struct _reent *<[rptr]>;
  27         int <[fd]>;
  28         const void *<[buf]>;
  29         size_t <[n]>;
  30         off_t <[off]>;
  31
  32 DESCRIPTION
  33 The <<pwrite>> function is similar to <<write>>.  One difference is that
  34 <<pwrite>> has an additional parameter <[off]> which is the offset to
  35 position in the file before writing.  The function also differs in that
  36 the file position is unchanged by the function (i.e. the file position
  37 is the same before and after a call to <<pwrite>>).
  38
  39 The <<_pwrite_r>> function is the same as <<pwrite>>, only a reentrant
  40 struct pointer <[rptr]> is provided to preserve reentrancy.
  41
  42 RETURNS
  43 <<pwrite>> returns the number of bytes written or <<-1>> if failure occurred.
  44
  45 PORTABILITY
  46 <<pwrite>> is non-ANSI and is specified by the Single Unix Specification.
  47
  48 Supporting OS subroutine required: <<write>>, <<lseek>>.
  49 */
  50
  51 #include <_ansi.h>
  52 #include <unistd.h>
  53 #include <reent.h>
  54
  55 ssize_t
  56 _DEFUN (_pwrite_r, (rptr, fd, buf, n, off),
  57      struct _reent *rptr _AND
  58      int fd _AND
  59      _CONST _PTR buf _AND
  60      size_t n _AND
  61      off_t off)
  62 {
  63   off_t cur_pos;
  64   _READ_WRITE_RETURN_TYPE num_written;
  65
  66   if ((cur_pos = _lseek_r (rptr, fd, 0, SEEK_CUR)) == (off_t)-1)
  67     return -1;
  68
  69   if (_lseek_r (rptr, fd, off, SEEK_SET) == (off_t)-1)
  70     return -1;
  71
  72   num_written = _write_r (rptr, fd, buf, n);
  73
  74   if (_lseek_r (rptr, fd, cur_pos, SEEK_SET) == (off_t)-1)
  75     return -1;
  76
  77   return (ssize_t)num_written;
  78 }
  79
  80 #ifndef _REENT_ONLY
  81
  82 ssize_t
  83 _DEFUN (pwrite, (fd, buf, n, off),
  84      int fd _AND
  85      _CONST _PTR buf _AND
  86      size_t n _AND
  87      off_t off)
  88 {
  89   return _pwrite_r (_REENT, fd, buf, n, off);
  90 }
  91
  92 #endif