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# QValidator Class Reference

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

    #include <QValidator>

Part of the QtGui module.

Inherits QObject.

Inherited by QDoubleValidator, QIntValidator, and QRegExpValidator.

- List of all members, including inherited members
- Qt 3 support members

### Public Types

- enum State { Invalid, Intermediate, Acceptable }

### Public Functions

- QValidator ( QObject * parent )
- ~QValidator ()
- virtual void fixup ( QString & input ) const
- virtual State validate ( QString & input, int & pos ) const = 0

- 28 public functions inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 1 signal inherited from QObject
- 4 static public members inherited from QObject
- 7 protected functions inherited from QObject

## 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`.

QValidator is typically used with QLineEdit, QSpinBox and QComboBox.

## Member Type Documentation

### enum QValidator::State

This enum type defines the states in which a validated string can exist.

Constant | Value | Description
--- | --- | ---
`QValidator::Invalid` | `0` | The string is clearly invalid.
`QValidator::Intermediate` | `1` | The string is a plausible intermediate value during editing.
`QValidator::Acceptable` |  | The string is acceptable as a final result; i.e. it is valid.

## Member Function Documentation

### QValidator::QValidator ( QObject * parent )

Sets up the validator. The parent parameter is passed on to the QObject constructor.

### QValidator::~QValidator ()

Destroys the validator, freeing any storage and other resources used.

### void QValidator::fixup ( QString & input ) const `[virtual]`

This function attempts to change input 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.

Reimplementations of this function can change input 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.

### State QValidator::validate ( QString & input, int & pos ) const `[pure virtual]`

This virtual function returns `Invalid` if input 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.

The function can change both input and pos (the cursor position) if required.