path: root/doc/qmemarray.doc

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/*****************************************************************************
  QMemArray documentation
 *****************************************************************************/

/*!
    \class QMemArray qmemarray.h
    \reentrant
    \brief The QMemArray class is a template class that provides arrays of simple types.

    \ingroup tools

    QMemArray is implemented as a template class. Define a template
    instance QMemArray\<X\> to create an array that contains X items.

    QMemArray stores the array elements directly in the array. It can
    only deal with simple types (i.e. C++ types, structs, and classes
    that have no constructors, destructors, or virtual functions).
    QMemArray uses bitwise operations to copy and compare array
    elements. 

    The QPtrVector collection class is also a kind of array. Like most
    \link collection.html collection classes\endlink, it uses pointers
    to the contained items.

    QMemArray uses \link shclass.html explicit sharing\endlink with a
    reference count. If more than one array shares common data and one
    of the arrays is modified, all the arrays are modified.

    The benefit of sharing is that a program does not need to duplicate
    data when it is not required, which results in lower memory use
    and less copying of data.

    An alternative to QMemArray is QValueVector. The QValueVector class
    also provides an array of objects, but can deal with objects that
    have constructors (specifically a copy constructor and a default
    constructor). QValueVector provides an STL-compatible syntax and is
    \link shclass.html implicitly shared\endlink.

    Example:
    \code
    #include <qmemarray.h>
    #include <stdio.h>

    QMemArray<int> fib( int num ) // returns fibonacci array
    {
	Q_ASSERT( num > 2 );
	QMemArray<int> f( num ); // array of ints

	f[0] = f[1] = 1;
	for ( int i = 2; i < num; i++ )
	    f[i] = f[i-1] + f[i-2];

	return f;
    }

    int main()
    {
	QMemArray<int> a = fib( 6 ); // get first 6 fibonaccis
	for ( int i = 0; i < a.size(); i++ )
	    qDebug( "%d: %d", i, a[i] );

	qDebug( "1 is found %d times", a.contains(1) );
	qDebug( "5 is found at index %d", a.find(5) );

	return 0;
    }
    \endcode

    Program output:
    \code
    0: 1
    1: 1
    2: 2
    3: 3
    4: 5
    5: 8
    1 is found 2 times
    5 is found at index 4
    \endcode

    Note concerning the use of QMemArray for manipulating structs or
    classes: Compilers will often pad the size of structs of odd sizes
    up to the nearest word boundary. This will then be the size
    QMemArray will use for its bitwise element comparisons. Because
    the remaining bytes will typically be uninitialized, this can
    cause find() etc. to fail to find the element. Example:

    \code
    // MyStruct may be padded to 4 or 8 bytes
    struct MyStruct
    {
	short i; // 2 bytes
	char c;  // 1 byte
    };

    QMemArray<MyStruct> a(1);
    a[0].i = 5;
    a[0].c = 't';

    MyStruct x;
    x.i = '5';
    x.c = 't';
    int i = a.find( x ); // may return -1 if the pad bytes differ
    \endcode

    To work around this, make sure that you use a struct where
    sizeof() returns the same as the sum of the sizes of the members
    either by changing the types of the struct members or by adding
    dummy members.

    QMemArray data can be traversed by iterators (see begin() and
    end()). The number of items is returned by count(). The array can
    be resized with resize() and filled using fill().

    You can make a shallow copy of the array with assign() (or
    operator=()) and a deep copy with duplicate().

    Search for values in the array with find() and contains(). For
    sorted arrays (see sort()) you can search using bsearch().

    You can set the data directly using setRawData() and
    resetRawData(), although this requires care.

    \sa \link shclass.html Shared Classes\endlink
*/

/*! \enum QMemArray::Iterator
    A QMemArray iterator.
    \sa begin() end()
*/
/*! \enum QMemArray::ConstIterator
    A const QMemArray iterator.
    \sa begin() end()
*/
/*! \enum QMemArray::ValueType
    \internal
*/

/*!
    \fn QMemArray::QMemArray()

    Constructs a null array.

    \sa isNull()
*/

/*!
    \fn QMemArray::QMemArray( int size )

    Constructs an array with room for \a size elements. Makes a null
    array if \a size == 0.

    The elements are left uninitialized.

    \sa resize(), isNull()
*/

/*!
    \fn QMemArray::QMemArray( const QMemArray<type> &a )

    Constructs a shallow copy of \a a.

    \sa assign()
*/

/*!
    \fn QMemArray::QMemArray( int, int )

    Constructs an array \e{without allocating} array space. The
    arguments should be (0, 0). Use at your own risk.
*/

/*!
    \fn QMemArray::~QMemArray()

    Dereferences the array data and deletes it if this was the last
    reference.
*/

/*!
    \fn QMemArray<type> &QMemArray::operator=( const QMemArray<type> &a )

    Assigns a shallow copy of \a a to this array and returns a
    reference to this array.

    Equivalent to assign( a ).
*/

/*!
    \fn type *QMemArray::data() const

    Returns a pointer to the actual array data.

    The array is a null array if data() == 0 (null pointer).

    \sa isNull()
*/

/*!
    \fn uint QMemArray::nrefs() const

    Returns the reference count for the shared array data. This
    reference count is always greater than zero.
*/

/*!
    \fn uint QMemArray::size() const

    Returns the size of the array (maximum number of elements).

    The array is a null array if size() == 0.

    \sa isNull(), resize()
*/

/*!
    \fn uint QMemArray::count() const

    Returns the same as size().

    \sa size()
*/

/*!
    \fn bool QMemArray::isEmpty() const

    Returns TRUE if the array is empty; otherwise returns FALSE.

    isEmpty() is equivalent to isNull() for QMemArray (unlike
    QString).
*/

/*!
    \fn bool QMemArray::isNull() const

    Returns TRUE if the array is null; otherwise returns FALSE.

    A null array has size() == 0 and data() == 0.
*/

/*!
    \fn bool QMemArray::resize( uint size, Optimization optim )

    Resizes (expands or shrinks) the array to \a size elements. The
    array becomes a null array if \a size == 0.

    Returns TRUE if successful, or FALSE if the memory cannot be
    allocated.

    New elements are not initialized.

    \a optim is either \c QGArray::MemOptim (the default) or
    \c QGArray::SpeedOptim.

    <b>Note:</b> By default, \c SpeedOptim is not available for general
    use since it is only available if Qt is built in a particular
    configuration.

    \sa size()
*/

/*!
    \fn bool QMemArray::resize( uint size )

    \overload

    Resizes (expands or shrinks) the array to \a size elements. The
    array becomes a null array if \a size == 0.

    Returns TRUE if successful, i.e. if the memory can be allocated;
    otherwise returns FALSE.

    New elements are not initialized.

    \sa size()
*/

/*!
    \fn bool QMemArray::truncate( uint pos )

    Truncates the array at position \a pos.

    Returns TRUE if successful, i.e. if the memory can be allocated;
    otherwise returns FALSE.

    Equivalent to resize(\a pos).

    \sa resize()
*/

/*!
    \fn bool QMemArray::fill( const type &v, int size )

    Fills the array with the value \a v. If \a size is specified as
    different from -1, then the array will be resized before being
    filled.

    Returns TRUE if successful, i.e. if \a size is -1, or \a size is
    != -1 and the memory can be allocated; otherwise returns FALSE.

    \sa resize()
*/

/*!
    \fn void QMemArray::detach()

    Detaches this array from shared array data; i.e. it makes a
    private, deep copy of the data.

    Copying will be performed only if the \link nrefs() reference
    count\endlink is greater than one.

    \sa copy()
*/

/*!
    \fn QMemArray<type> QMemArray::copy() const

    Returns a deep copy of this array.

    \sa detach(), duplicate()
*/

/*!
    \fn QMemArray<type> &QMemArray::assign( const QMemArray<type> &a )

    Shallow copy. Dereferences the current array and references the
    data contained in \a a instead. Returns a reference to this array.

    \sa operator=()
*/

/*!
    \fn QMemArray<type> &QMemArray::assign( const type *data, uint size )

    \overload

    Shallow copy. Dereferences the current array and references the
    array data \a data, which contains \a size elements. Returns a
    reference to this array.

    Do not delete \a data later; QMemArray will call free() on it
    at the right time.
*/

/*!
    \fn QMemArray<type> &QMemArray::duplicate( const QMemArray<type> &a )

    Deep copy. Dereferences the current array and obtains a copy of
    the data contained in \a a instead. Returns a reference to this
    array.

    \sa copy()
*/

/*!
    \fn QMemArray<type> &QMemArray::duplicate( const type *data, uint size )

    \overload

    Deep copy. Dereferences the current array and obtains a copy of
    the array data \a data instead. Returns a reference to this array.
    The size of the array is given by \a size.

    \sa copy()
*/

/*!
    \fn QMemArray<type> &QMemArray::setRawData( const type *data, uint size )

    Sets raw data and returns a reference to the array.

    Dereferences the current array and sets the new array data to \a
    data and the new array size to \a size. Do not attempt to resize
    or re-assign the array data when raw data has been set. Call
    resetRawData(\a data, \a size) to reset the array.

    Setting raw data is useful because it sets QMemArray data without
    allocating memory or copying data.

    Example I (intended use):
    \code
    static char bindata[] = { 231, 1, 44, ... };
    QByteArray	a;
    a.setRawData( bindata, sizeof(bindata) );	// a points to bindata
    QDataStream s( a, IO_ReadOnly );		// open on a's data
    s >> <something>;				// read raw bindata
    a.resetRawData( bindata, sizeof(bindata) ); // finished
    \endcode

    Example II (you don't want to do this):
    \code
    static char bindata[] = { 231, 1, 44, ... };
    QByteArray	a, b;
    a.setRawData( bindata, sizeof(bindata) );	// a points to bindata
    a.resize( 8 );				// will crash
    b = a;					// will crash
    a[2] = 123;					// might crash
    // forget to resetRawData: will crash
    \endcode

    \warning If you do not call resetRawData(), QMemArray will attempt
    to deallocate or reallocate the raw data, which might not be too
    good. Be careful.

    \sa resetRawData()
*/

/*!
    \fn void QMemArray::resetRawData( const type *data, uint size )

    Removes internal references to the raw data that was set using
    setRawData(). This means that QMemArray no longer has access to
    the \a data, so you are free to manipulate \a data as you wish.
    You can now use the QMemArray without affecting the original \a
    data, for example by calling setRawData() with a pointer to some
    other data.

    The arguments must be the \a data and length, \a size, that were
    passed to setRawData(). This is for consistency checking.

    \sa setRawData()
*/

/*!
    \fn int QMemArray::find( const type &v, uint index ) const

    Finds the first occurrence of \a v, starting at position \a index.

    Returns the position of \a v, or -1 if \a v could not be found.

    \sa contains()
*/

/*!
    \fn int QMemArray::contains( const type &v ) const

    Returns the number of times \a v occurs in the array.

    \sa find()
*/

/*!
    \fn void QMemArray::sort()

    Sorts the array elements in ascending order, using bitwise
    comparison (memcmp()).

    \sa bsearch()
*/

/*!
    \fn int QMemArray::bsearch( const type &v ) const

    In a sorted array (as sorted by sort()), finds the first
    occurrence of \a v by using a binary search. For a sorted
    array this is generally much faster than find(), which does
    a linear search.

    Returns the position of \a v, or -1 if \a v could not be found.

    \sa sort(), find()
*/

/*!
    \fn type &QMemArray::operator[]( int index ) const

    Returns a reference to the element at position \a index in the
    array.

    This can be used to both read and set an element. Equivalent to
    at().

    \sa at()
*/

/*!
    \fn type &QMemArray::at( uint index ) const

    Returns a reference to the element at position \a index in the array.

    This can be used to both read and set an element.

    \sa operator[]()
*/

/*!
    \fn QMemArray::operator const type *() const

    Cast operator. Returns a pointer to the array.

    \sa data()
*/

/*!
    \fn bool QMemArray::operator==( const QMemArray<type> &a ) const

    Returns TRUE if this array is equal to \a a; otherwise returns
    FALSE.

    The two arrays are compared bitwise.

    \sa operator!=()
*/

/*!
    \fn bool QMemArray::operator!=( const QMemArray<type> &a ) const

    Returns TRUE if this array is different from \a a; otherwise
    returns FALSE.

    The two arrays are compared bitwise.

    \sa operator==()
*/

/*!
    \fn Iterator QMemArray::begin()

    Returns an iterator pointing at the beginning of this array. This
    iterator can be used in the same way as the iterators of
    QValueList and QMap, for example.
*/

/*!
    \fn Iterator QMemArray::end()

    Returns an iterator pointing behind the last element of this
    array. This iterator can be used in the same way as the iterators
    of QValueList and QMap, for example.
*/

/*!
    \fn ConstIterator QMemArray::begin() const

    \overload

    Returns a const iterator pointing at the beginning of this array.
    This iterator can be used in the same way as the iterators of
    QValueList and QMap, for example.
*/

/*!
    \fn ConstIterator QMemArray::end() const

    \overload

    Returns a const iterator pointing behind the last element of this
    array. This iterator can be used in the same way as the iterators
    of QValueList and QMap, for example. 
*/