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# QValidator Class Reference
[com.trolltech.qt.gui module]

The `QValidator` class provides validation of input text. More...

Inherits `QObject`.

Inherited by `QDoubleValidator`, `QIntValidator`, and `QRegExpValidator`.

## Detailed Description

The `QValidator` class provides validation of input text.

The class itself is abstract. Two subclasses, `QIntValidator` and `QDoubleValidator`, provide basic numeric-range checking, and `QRegExpValidator` provides general checking using a custom regular expression.

If the built-in validators aren't sufficient, you can subclass `QValidator`. The class has two virtual functions: `validate` and `fixup`.

`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 clearly invalid. Intermediate is less obvious: the concept of validity is difficult to apply when the string is incomplete (still being edited). `QValidator` 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.

Here are some examples:

- For a line edit that accepts integers from 10 to 999 inclusive, 42 and 123 are Acceptable, the empty string and 5 are Intermediate, and "asdf" and 1114 is Invalid.
- 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 action 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.
- 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. `QLineEdit`, 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.

A validator has a locale, set with `setLocale`. It is typically used to parse localized data. For example, `QIntValidator` and `QDoubleValidator` use it to parse localized representations of integers and doubles.

`QValidator` is typically used with `QLineEdit`, `QSpinBox` and `QComboBox`.

See also `QIntValidator`, `QDoubleValidator`, `QRegExpValidator`, and Line Edits Example.