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| XmtSymbolAddCallback(3) | FreeBSD Library Functions Manual | XmtSymbolAddCallback(3) |
NAME
XmtSymbolAddCallback(), XmtSymbolRemoveCallback() - add and remove a procedure to be called when a symbol's value changes.SYNOPSIS
void XmtSymbolAddCallback(XmtSymbol s, XmtSymbolCallbackProc proc, XtPointer client_data)
void XmtSymbolRemoveCallback(XmtSymbol s, XmtSymbolCallbackProc proc, XtPointer client_data)
typedef void (*XmtSymbolCallbackProc)(XmtSymbol s, XtPointer client_data, XtArgVal value);
ARGUMENTS
INPUTS- s
- An XmtSymbol for which the callback is to be added or removed.
- proc
- The procedure to be added or removed.
- client_data
- An untyped data value registered (or removed) with proc, and which is passed as the second argument to proc when it is invoked.
- value
- The untyped value of the symbol. This argument is not passed to XmtSymbolAddCallback() or XmtSymbolRemoveCallback(), but it is the third argument passed to the registered XmtSymbolCallbackProc proc when it is invoked.
DESCRIPTION
XmtSymbolAddCallback() registers the procedure proc to be invoked with the specified client_data whenever the value of symbol s changes.XmtSymbolRemoveCallback() unregisters the proc/client_data pair for symbol s. This procedure will no longer be called with the specified client_data when the value of s is updated.
proc is an XmtSymbolCallbackProc. It will be invoked with three arguments. The first argument to a symbol callback is the XmtSymbol that has had its value changed. The second argument is whatever untyped client_data was registered with the callback procedure, and the third argument, value, is the new value of the symbol. This is either the value itself, or, if the value is too large to fit in an XtArgVal (or if it is of type XmtRBuffer), it is a pointer to the value.
SEE ALSO
Chapter 12, Symbols,XmtLookupSymbol(), XmtSymbolGetValue(), XmtSymbolSetValue(), XmtSymbolSetTypedValue(), XmtVaRegisterSymbols().
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