https://invisible-island.net/xterm/xtoolkit/
XtAppAddInput, XtRemoveInput - register and remove an input source
#include <X11/Intrinsic.h>
XtInputId XtAppAddInput(XtAppContext app_context, int source, XtPointer
condition, XtInputCallbackProc proc, XtPointer client_data);
void XtRemoveInput(XtInputId id);
app_context
Specifies the application context that identifies the appli-
cation.
client_data
Specifies the argument that is to be passed to the specified
procedure when input is available.
condition Specifies the mask that indicates a read, write, or exception
condition or some operating system dependent condition.
id Specifies the ID returned from the corresponding XtAppAdd-
Input call.
proc Specifies the procedure that is to be called when input is
available.
source Specifies the source file descriptor on a UNIX-based system
or other operating system dependent device specification.
The XtAppAddInput function registers with the Intrinsics read routine a
new source of events, which is usually file input but can also be file
output. Note that file should be loosely interpreted to mean any sink
or source of data. XtAppAddInput also specifies the conditions under
which the source can generate events. When input is pending on this
source, the callback procedure is called.
The legal values for the condition argument are operating-system depen-
dent. On a UNIX-based system, the condition is some union of XtInpu-
tReadMask, XtInputWriteMask, and XtInputExceptMask. The XtRemoveInput
function causes the Intrinsics read routine to stop watching for input
from the input source.
XtAppAddTimeOut(3),XtAppAddSignal(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
In ANSI C it is necessary to cast the condition to an XtPointer, e.g.:
XtAppAddInput(app_context,
source,
(XtPointer) (XtInputReadMask | XtInputWriteMask),
proc,
client_data);
X Version 11 libXt 1.1.5.2 XtAppAddInput(3)