The class itself is abstract. Two subclasses, QIntValidator and TQDoubleValidator, provide basic numeric-range checking, and TQRegExpValidator provides general checking using a custom regular expression.
validate() must be implemented by every subclass. It returns Invalid, Intermediate or Acceptable depending on whether its argument is valid (for the subclass's definition of valid).
These three states require some explanation. An Invalid string is \fIclearly\fR invalid. Intermediate is less obvious: the concept of validity is slippery when the string is incomplete (still being edited). TQValidator defines Intermediate as the property of a string that is neither clearly invalid nor acceptable as a final result. Acceptable means that the string is acceptable as a final result. One might say that any string that is a plausible intermediate state during entry of an Acceptable string is Intermediate.
For a line edit that accepts integers from 0 to 999 inclusive, 42 and 123 are Acceptable, the empty string and 1114 are Intermediate and asdf is Invalid.
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For an editable combobox that accepts URLs, any well-formed URL is Acceptable, "http://www.trolltech.com/," is Intermediate (it might be a cut and paste operation that accidentally took in a comma at the end), the empty string is Intermediate (the user might select and delete all of the text in preparation for entering a new URL), and "http:///./" is Invalid.
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For a spin box that accepts lengths, "11cm" and "1in" are Acceptable, "11" and the empty string are Intermediate and" http://www.trolltech.com" and "hour" are Invalid.
fixup() is provided for validators that can repair some user errors. The default implementation does nothing. TQLineEdit, for example, will call fixup() if the user presses Enter (or Return) and the content is not currently valid. This allows the fixup() function the opportunity of performing some magic to make an Invalid string Acceptable.
This function attempts to change \fIinput\fR to be valid according to this validator's rules. It need not result in a valid string: callers of this function must re-test afterwards; the default does nothing.
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Reimplementations of this function can change \fIinput\fR even if they do not produce a valid string. For example, an ISBN validator might want to delete every character except digits and "-", even if the result is still not a valid ISBN; a surname validator might want to remove whitespace from the start and end of the string, even if the resulting string is not in the list of accepted surnames.
This pure virtual function returns Invalid if \fIinput\fR is invalid according to this validator's rules, Intermediate if it is likely that a little more editing will make the input acceptable (e.g. the user types '4' into a widget which accepts integers between 10 and 99) and Acceptable if the input is valid.
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The function can change \fIinput\fR and \fIpos\fR (the cursor position) if it wants to.
