QExpressionEvaluator Class Reference
[QtBaseModule]

Valuespace integration

The expression evaluator has the ability to use values from the Qt Extended valuespace in its expressions.

    2 + @/Value/Space/Key

The above code would add 2 and the value for /Value/Space/Key in the valuespace.

The '@' character uniquely identifies the subsequent characters as a valuespace key to the expression evaluator.

In the above example, /Value/Space/Key must return data that can be converted to an integer. If conversion fails, a run-time error will occur and evaluate() will return false.

If a value in the valuespace changes, expressions which use that value will emit the termsChanged() signal.

Member Type Documentation

enum QExpressionEvaluator::FloatingPointFormat

Controls the floating point format used by the expression evaluator.

Member Function Documentation

QExpressionEvaluator::QExpressionEvaluator ( QObject * parent = 0 )

Constructs a QExpressionEvaluator. parent is passed to the QObject constructor.

QExpressionEvaluator::QExpressionEvaluator ( const QByteArray & expr, QObject * parent = 0 )

Constructs a QExpressionEvaluator.

expr is passed to setExpression(). parent is passed to the QObject constructor.

QExpressionEvaluator::~QExpressionEvaluator ()

Destroys the QExpressionEvaluator.

void QExpressionEvaluator::clear ()   [slot]

Clears the set expression and any associated data structures.

The expression becomes invalid ie. isValid() returns false.

bool QExpressionEvaluator::evaluate ()

Evaluates the expression specified through setExpression().

isValid() must return true before you call this function, otherwise it will abort().

Returns true if the expression was successfully evaluated, or false if a run-time error occured.

A run-time error can occur due to a coercion error or divide by zero.

If this function returns true, the result of the evaluation can be retrieved using result().

QByteArray QExpressionEvaluator::expression () const

Returns the current expression data the evaluator is operating on.

See also setExpression().

FloatingPointFormat QExpressionEvaluator::floatingPointFormat () const

Returns the current floating point format.

See also setFloatingPointFormat().

bool QExpressionEvaluator::isValid () const

Returns true if this expression is valid, otherwise false.

An expression is valid if it is not empty, it is syntactually and semantically correct, and a previous call to evaluate() did not result in a run-time error.

You must not call evaluate() unless this function returns true.

QVariant QExpressionEvaluator::result ()

Returns the result of the last call to evaluate() as a QVariant.

Returns an empty QVariant if evaluate() has not yet been called.

bool QExpressionEvaluator::setExpression ( const QByteArray & expr )   [slot]

Sets the expression for the evaluator to be expr

expr is parsed and semantically checked immediat

Returns true on success; otherwise returns false.

You should call isValid() after this function to determine whether the setup phase was completed successfully.

See also expression().

void QExpressionEvaluator::setFloatingPointFormat ( const FloatingPointFormat & fmt )

Sets the floating point format to be used by the expression evaluator to fmt.

The default is QExpressionEvaluator::Double, but setting QExpressionEvaluator::FixedPoint may give results appropriate for user level applications.

See also floatingPointFormat().

void QExpressionEvaluator::termsChanged ()   [signal]

Emitted when a pluggable term in the expression changes.