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WTSupported in traditional Synergy on Windows
WNSupported in Synergy .NET on Windows
USupported on UNIX
VSupported on OpenVMS
xcall CHNOPN(channel, status)
The expression that contains the channel you want to check. (n)
Returned with one of the following values: (n)
1 = The channel is in use.
0 = The channel is closed.
The CHNOPN subroutine checks whether a channel is in use by an open file. CHNOPN is functionally identical to DBL$CHOPEN.
The following program opens a specified file on the first available channel.
.define TTCHN ,1 record filename ,a20 ;Filename to open chn ,d4 ;Channel to open proc open(TTCHN, o, "tt:") xcall flags(4020) do forever begin display(TTCHN, "Enter a filename to open: ") reads(TTCHN, filename) xcall openit(filename, chn) if (chn) writes(TTCHN, "Opened " + filename + "on channel #" + %a(chn)) end ;End of do forever loop end ;End of main routine subroutine openit ;Find an available channel a_file ,a ;Contains name of file to open a_rchn ,d ;Returned with next available channel record stat ,d1 ;Used with XCALL CHNOPN proc for a_rchn from 2 thru 1024 begin xcall chnopn(a_rchn, stat) if (.not.stat) begin open(a_rchn, i, a_file) [err=nofile] xreturn end end operr, writes(TTCHN, "Exceeds maximum channels " + a_file) goto oprtn nofile, writes(TTCHN, "Cannot open " + a_file) oprtn, clear a_rchn xreturn endsubroutine