User guide

52 CHAPTER 3. THE LIBRARY

block (TCB) is unlinked from the priority chain and removed from tasktab. Finally

its segment list and the TCB itself return ed to free store. It returns a non zero value

if successful. On failure, it returns zero with result2 set t o 101 if taskid is invalid, or

to 108 i f the task is not deletabl e.

res := dqpkt(id, pkt) CIN:n, POS:y, NAT:n

This Cintpos function attempts to dequeue the given packet from the task or device

speciﬁed by id. If not found there, it may have already been returned to the current

task so its work queue is searched. The result is the id of the task or device whose

work queue contained the packet. If there is an error, the resu l t is zero with result2

set to 101 for invalid id or 109 if the packet was not found. The id ﬁeld of the packet

is set to the id of the task or device whose work queue contained the packet provided

that this is not the id of the current task .

endread() CIN:y, POS:y, NAT:y

This routine closes the currently s el e c te d input stream by calling endstream(cis).

endstream(scb) CIN:y, POS:y, NAT:y

This routine closes the stream whose control block is scb.

endwrite() CIN:y, POS:y, NAT:y

This routine closes the currently selected output stream by cal l i ng endstream(cos).

scb := findappend(name) CIN:y, POS:y, NAT:y

This function opens an output stream speciﬁed by the ﬁle name name in append

mode causing all output t o b e appended onto the end of the ﬁle. If the ﬁle name is

relative and the preﬁx string is set, it is prepended to the name before attempting to

open the stream. If the ﬁle does not exist a zero length ﬁle of the given name is created.

If there is an error the result is zero.

n := findarg(keys, item) CIN:y, POS:y, NAT:y

The function findarg was primari l y designed for use by rdargs but since it is

sometimes use fu l on its own, it is publicly available. Its ﬁrst argument, keys, i s a string

of keys of the form used by rdargs and item is a stri ng. If t he result is positive, it

is the argument number of the keyword that matches item, otherwise the result is -1.

During matching all letters are converted to uppercase, but this convention may change

in future.

scb := findinput(name) CIN:y, POS:y, NAT:y

This function opens an input stream. If name is the string "*" then it opens the

standard input stream which is normally from the keyboard, otherwise name is taken

to be a device or ﬁle name. If the ﬁle name is relative and the preﬁx string is s et , it

is prepended to the name before attempting to open the stream. If the stream cannot

be opened the result i s zero. See Section 3.3.2 for information about the treatment of

ﬁlenames.

scb := findoutput(name) CIN:y, POS:y, NAT:y

This function opens an output stream speciﬁed by the device or ﬁle name name. I f