I/O Channels

PRO/5 uses the input/output channel approach to file access. The OPEN verb is used to "attach" a file to a programmer-selected channel number. All subsequent I/O with that file uses that channel number. When all desired I/O with that file is complete, the CLOSE verb is used to disassociate the channel with the file. The channel may then be reused for another file. The number of channels available determines the number of files that may be accessed at one time. PRO/5 will allow as many channels as the host operating system. PRO/5 cannot exceed the limits imposed by the host system.

In PRO/5 the programmer selects the channel numbers to use. Any integer from 1 to 32767 may be used for a channel number. Channel 0 is also a valid channel. However, it is always open, usually to your terminal and keyboard, and it cannot be closed or reassigned.