[444] | 1 | #ifndef _NO_PREAD |
---|
| 2 | /* |
---|
| 3 | FUNCTION |
---|
| 4 | <<pread>>---read a file from specified position |
---|
| 5 | |
---|
| 6 | INDEX |
---|
| 7 | pread |
---|
| 8 | INDEX |
---|
| 9 | _pread_r |
---|
| 10 | |
---|
| 11 | SYNOPSIS |
---|
| 12 | #include <unistd.h> |
---|
| 13 | ssize_t pread(int <[fd]>, void *<[buf]>, size_t <[n]>, off_t <[off]>); |
---|
| 14 | ssize_t _pread_r(struct _reent *<[rptr]>, int <[fd]>, |
---|
| 15 | void *<[buf]>, size_t <[n]>, off_t <[off]>); |
---|
| 16 | |
---|
| 17 | DESCRIPTION |
---|
| 18 | The <<pread>> function is similar to <<read>>. One difference is that |
---|
| 19 | <<pread>> has an additional parameter <[off]> which is the offset to |
---|
| 20 | position in the file before reading. The function also differs in that |
---|
| 21 | the file position is unchanged by the function (i.e. the file position |
---|
| 22 | is the same before and after a call to <<pread>>). |
---|
| 23 | |
---|
| 24 | The <<_pread_r>> function is the same as <<pread>>, only a reentrant |
---|
| 25 | struct pointer <[rptr]> is provided to preserve reentrancy. |
---|
| 26 | |
---|
| 27 | RETURNS |
---|
| 28 | <<pread>> returns the number of bytes read or <<-1>> if failure occurred. |
---|
| 29 | |
---|
| 30 | PORTABILITY |
---|
| 31 | <<pread>> is non-ANSI and is specified by the Single Unix Specification. |
---|
| 32 | |
---|
| 33 | Supporting OS subroutine required: <<read>>, <<lseek>>. |
---|
| 34 | */ |
---|
| 35 | |
---|
| 36 | #include <_ansi.h> |
---|
| 37 | #include <unistd.h> |
---|
| 38 | #include <reent.h> |
---|
| 39 | |
---|
| 40 | ssize_t |
---|
| 41 | _pread_r (struct _reent *rptr, |
---|
| 42 | int fd, |
---|
| 43 | void *buf, |
---|
| 44 | size_t n, |
---|
| 45 | off_t off) |
---|
| 46 | { |
---|
| 47 | off_t cur_pos; |
---|
| 48 | _READ_WRITE_RETURN_TYPE num_read; |
---|
| 49 | |
---|
| 50 | if ((cur_pos = _lseek_r (rptr, fd, 0, SEEK_CUR)) == (off_t)-1) |
---|
| 51 | return -1; |
---|
| 52 | |
---|
| 53 | if (_lseek_r (rptr, fd, off, SEEK_SET) == (off_t)-1) |
---|
| 54 | return -1; |
---|
| 55 | |
---|
| 56 | num_read = _read_r (rptr, fd, buf, n); |
---|
| 57 | |
---|
| 58 | if (_lseek_r (rptr, fd, cur_pos, SEEK_SET) == (off_t)-1) |
---|
| 59 | return -1; |
---|
| 60 | |
---|
| 61 | return (ssize_t)num_read; |
---|
| 62 | } |
---|
| 63 | |
---|
| 64 | #ifndef _REENT_ONLY |
---|
| 65 | |
---|
| 66 | ssize_t |
---|
| 67 | pread (int fd, |
---|
| 68 | void *buf, |
---|
| 69 | size_t n, |
---|
| 70 | off_t off) |
---|
| 71 | { |
---|
| 72 | return _pread_r (_REENT, fd, buf, n, off); |
---|
| 73 | } |
---|
| 74 | |
---|
| 75 | #endif /* !_REENT_ONLY */ |
---|
| 76 | #endif /* !_NO_PREAD */ |
---|