https://invisible-island.net/xterm/xtoolkit/
XtConvert, XtDirectConvert - invoke resource converters
#include <X11/Intrinsic.h>
void XtConvert(Widget w, const char *from_type, XrmValuePtr from, const
char *to_type, XrmValuePtr to_return);
void XtDirectConvert(XtConverter converter, XrmValuePtr args, Cardinal
num_args, XrmValuePtr from, XrmValuePtr to_return);
args Specifies the argument list that contains the additional
arguments needed to perform the conversion (often NULL).
converter Specifies the conversion procedure that is to be called.
from Specifies the value to be converted.
from_type Specifies the source type.
num_args Specifies the number of additional arguments (often zero).
to_type Specifies the destination type.
to_return Returns the converted value.
w Specifies the widget to use for additional arguments (if any
are needed).
The XtConvert function looks up the type converter registered to con-
vert from_type to to_type, computes any additional arguments needed,
and then calls XtDirectConvert. XtConvert has been replaced by XtCon-
vertAndStore.
The XtDirectConvert function looks in the converter cache to see if
this conversion procedure has been called with the specified arguments.
If so, it returns a descriptor for information stored in the cache;
otherwise, it calls the converter and enters the result in the cache.
Before calling the specified converter, XtDirectConvert sets the return
value size to zero and the return value address to NULL. To determine
if the conversion was successful, the client should check
to_return.address for non-NULL. XtDirectConvert has been replaced by
XtCallConverter.
XtAppAddConverter(3), XtStringConversionWarning(3), XtConvertAnd-
Store(3), XtCallConverter(3)
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtConvert(3)