RE: GtkEntry and numeric floating point input

["Vlietstra, Joe (NSSD)" <Joe Vlietstra ngc com>]

Neil Zanella <nzanella gmail com> wrote: 
> I've got a GtkEntry and I need to confine user input into this widget
> to numeric values which will fit into the underlying C data types.
> What is the best way to do this? If the values were only allowed to
> be integers I'd use a GtkSpinBox (I think that's what it's > called),
> but since they are now allowed to have decimal points etc...
> what should I do to be sure the user doesn't enter invalid data.
> What's the best way?

GtkSpinButton will work for both integer and floating-point numbers.
See "Example 2" in the API documentation at:
   http://developer.gnome.org/doc/API/2.0/gtk/GtkSpinButton.html

We use spin buttons in instrumentation control (power supplies,
RF sources, etc.).  Spin button range checking works well and our
operators like the up/down arrows.

There are three properties of spin buttons that you may need to think
about:
-- Non-numeric characters
   Default spin button behavior reacts to non-numeric keys.
   We've never found a use/benefit for this behavior (hex entry?).
   Use gtk_spin_button_set_numeric to ignore non-numeric characters.
   API documentation is contradictory (description of "numeric"
   parameter is opposite of function summary).  Set the "numeric"
   parameter to TRUE to ignore non-numeric characters.
-- Snap to tick
   Default spin button behavior allows operator to enter a value
   that is not on a "tick" (up/down arrow) boundary.  This is
   desirable most of the time but you may need to call
   gtk_spin_button_set_snap_to_ticks to change this behavior.
   Example: Resolution of RF synthesizer hardware is 0.02 dB.
   Synthesizer will accept commands at finer resolution and
   quietly change the RF output to the nearest 0.02 dB tick.
   Better to have the application snap to tick than the hardware.   
-- Update policy
   99% of the time the default policy (GTK_UPDATE_ALWAYS) is what
   you want.  The spin button will be able to display a value that
   isn't in the range of the adjustment.  This can be handy.
   Example:  Application will query the voltage level from a DC
   power supply during initialization and display it in the spin
   button; this voltage level may be out of range but you need to
   inform the operator of the actual level.

Joe Vlietstra