**CIGAL Reference Manual, Chapter 6 (RealTime): r_fread**
===== r_fread -- Read data from a file =====
**usage: r_fread  opflg eflag ltime Databuf Nbytes Lunit [Asyncflag]**

R_FREAD is a REALTIME operator. It initiates a data transfer of NBYTES from
the open file specified by LUNIT to the DATABUF variable. NBYTES is assumed
to be a long integer value.  LUNIT must have been previously set by a call
to R_FOPEN.  If LUNIT is missing it defaults to 1.

R_FREAD normally operates synchronously, not finishing until the data transfer
is completed.  To perform an asynchronous read, make ASYNCFLAG non-zero.  In
that case you should issue a R_FWAIT operation before assuming that the data
have all been read.

Note 1: If LUNIT is not an open file this operation returns immediately.
If a previous asynchronous I/O operation was still pending, this
operation will wait until that has completed before starting. This is
therefore equivalent to inserting a R_FWAIT operation.

Note 2: All REALTIME file I/O operations are performed asynchronously,
regardless of the ASYNCFLAG; this allows multiple independent
processing streams to continue while file data transfers are underway.
The ASYNCFLAG option therefore only specifies whether this particular
processing stream should wait until the I/O finishes.

**See Also:**\\
[[jvs:cigal|CIGAL Home]], 
[[jvs:cigal:manual|CIGAL Manual]], 
[[jvs:cigal:manual:chapter6|RealTime List]], 
[[jvs:cigal:manual:help|Manual Help]]