# aio_read

## NAME



           aio_read - asynchronous read
    


## LIBRARY



           Real-time library (_librt_ , _-lrt_)
    


## SYNOPSIS



           **#include <aio.h>**
    
           **int aio_read(struct aiocb ***_aiocbp_**);**
    


## DESCRIPTION



           The **aio_read**() function queues the I/O request described by the
           buffer pointed to by _aiocbp_.  This function is the asynchronous
           analog of read(2).  The arguments of the call
    
               read(fd, buf, count)
    
           correspond (in order) to the fields _aio_fildes_ , _aio_buf_ , and
           _aio_nbytes_ of the structure pointed to by _aiocbp_.  (See aio(7) for
           a description of the _aiocb_ structure.)
    
           The data is read starting at the absolute position
           _aiocbp- >aio_offset_, regardless of the file offset.  After the
           call, the value of the file offset is unspecified.
    
           The "asynchronous" means that this call returns as soon as the
           request has been enqueued; the read may or may not have completed
           when the call returns.  One tests for completion using
           aio_error(3).  The return status of a completed I/O operation can
           be obtained by aio_return(3).  Asynchronous notification of I/O
           completion can be obtained by setting _aiocbp- >aio_sigevent_
           appropriately; see sigevent(3type) for details.
    
           If **_POSIX_PRIORITIZED_IO** is defined, and this file supports it,
           then the asynchronous operation is submitted at a priority equal
           to that of the calling process minus _aiocbp- >aio_reqprio_.
    
           The field _aiocbp- >aio_lio_opcode_ is ignored.
    
           No data is read from a regular file beyond its maximum offset.
    


## RETURN VALUE



           On success, 0 is returned.  On error, the request is not enqueued,
           -1 is returned, and _errno_ is set to indicate the error.  If an
           error is detected only later, it will be reported via
           aio_return(3) (returns status -1) and aio_error(3) (error status—
           whatever one would have gotten in _errno_ , such as **EBADF**).
    


## ERRORS



           **EAGAIN** Out of resources.
    
           **EBADF** _aio_fildes_ is not a valid file descriptor open for reading.
    
           **EINVAL** One or more of _aio_offset_ , _aio_reqprio_ , or _aio_nbytes_ are
                  invalid.
    
           **ENOSYS aio_read**() is not implemented.
    
           **EOVERFLOW**
                  The file is a regular file, we start reading before end-of-
                  file and want at least one byte, but the starting position
                  is past the maximum offset for this file.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌──────────────────────────────────────┬───────────────┬─────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────────┼───────────────┼─────────┤
           │ **aio_read**()                           │ Thread safety │ MT-Safe │
           └──────────────────────────────────────┴───────────────┴─────────┘
    


## STANDARDS



           POSIX.1-2008.
    


## NOTES



           It is a good idea to zero out the control block before use.  The
           control block must not be changed while the read operation is in
           progress.  The buffer area being read into must not be accessed
           during the operation or undefined results may occur.  The memory
           areas involved must remain valid.
    
           Simultaneous I/O operations specifying the same _aiocb_ structure
           produce undefined results.
    


## EXAMPLES



           See aio(7).
    


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