63 lines
1.3 KiB
C
63 lines
1.3 KiB
C
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/*
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FUNCTION
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<<pread64>>---read a large file from specified position
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INDEX
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pread64
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ANSI_SYNOPSIS
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#include <unistd.h>
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ssize_t pread64(int <[fd]>, void *<[buf]>, size_t <[n]>, loff_t <[off]>);
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TRAD_SYNOPSIS
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#include <unistd.h>
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ssize_t pread64(<[fd]>, <[buf]>, <[n]>, <[off]>)
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int <[fd]>;
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void *<[buf]>;
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size_t <[n]>;
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loff_t <[off]>;
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DESCRIPTION
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The <<pread64>> function is similar to <<pread>>. The only difference is
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that it operates on large files and so takes a 64-bit offset. Like <<pread>>>,
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the file position is unchanged by the function (i.e. the file position
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is the same before and after a call to <<pread>>).
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RETURNS
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<<pread64>> returns the number of bytes read or <<-1>> if failure occurred.
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PORTABILITY
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<<pread64>> is an EL/IX extension.
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Supporting OS subroutine required: <<read64>>, <<lseek64>>.
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*/
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#include <_ansi.h>
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#include <unistd.h>
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#include <reent.h>
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ssize_t
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_DEFUN (pread64, (fd, buf, n, off),
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int fd _AND
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_PTR buf _AND
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size_t n _AND
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loff_t off)
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{
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loff_t cur_pos;
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_READ_WRITE_RETURN_TYPE num_read;
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if ((cur_pos = lseek64 (fd, 0, SEEK_CUR)) == (loff_t)-1)
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return -1;
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if (lseek64 (fd, off, SEEK_SET) == (loff_t)-1)
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return -1;
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num_read = read64 (fd, buf, n);
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if (lseek64 (fd, cur_pos, SEEK_SET) == (loff_t)-1)
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return -1;
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return (ssize_t)num_read;
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}
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