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    Command:

    pread

    
    
    
    

    SYNOPSIS

           #include <unistd.h>
    
           ssize_t pread(int fd, void *buf, size_t count, off_t offset);
    
           ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
    
       Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
    
           pread(), pwrite():
               _XOPEN_SOURCE >= 500
               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
    
    
    

    DESCRIPTION

           pread() reads up to count bytes from file descriptor fd at offset  off-
           set  (from the start of the file) into the buffer starting at buf.  The
           file offset is not changed.
    
           pwrite() writes up to count bytes from the buffer starting  at  buf  to
           the  file  descriptor  fd  at  offset  offset.   The file offset is not
           changed.
    
           The file referenced by fd must be capable of seeking.
    
    
    

    RETURN VALUE

           On success, the number of bytes read or written is returned (zero indi-
           cates  that  nothing  was  written,  in the case of pwrite(), or end of
           file, in the case of pread()), or -1 on error, in which case  errno  is
           set to indicate the error.
    
    
    

    ERRORS

           pread()  can  fail  and set errno to any error specified for read(2) or
           lseek(2).  pwrite() can fail and set errno to any error  specified  for
           write(2) or lseek(2).
    
    
    

    VERSIONS

           The  pread()  and  pwrite() system calls were added to Linux in version
           2.1.60; the entries in the i386 system call table were added in 2.1.69.
           C  library support (including emulation using lseek(2) on older kernels
           without the system calls) was added in glibc 2.1.
    
    
    

    CONFORMING TO

           POSIX.1-2001.
    
    
    

    NOTES

           The pread() and pwrite() system calls are especially useful  in  multi-
           threaded  applications.   They allow multiple threads to perform I/O on
           the same file descriptor without being affected by changes to the  file
           offset by other threads.
    
           On  Linux,  the  underlying  system  calls  were renamed in kernel 2.6:
           lseek(2), read(2), readv(2), write(2)
    
    
    

    Linux 2013-06-21 PREAD(2)

    
    
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