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