QMemArray(3qt)

NAME
QMemArray - Template class that provides arrays of simple types

SYNOPSIS
#include <qmemarray.h>

Inherited by QByteArray and QPointArray.

  Public Members
typedef type * Iterator
typedef const type * ConstIterator
QMemArray ()
QMemArray ( int size )
QMemArray ( const QMemArray<type> & a )
~QMemArray ()
QMemArray<type> & operator= ( const QMemArray<type> & a )
type * data () const
uint nrefs () const
uint size () const
uint count () const
bool isEmpty () const
bool isNull () const
bool resize ( uint size )
bool truncate ( uint pos )
bool fill ( const type & v, int size = -1 )
virtual void detach ()
QMemArray<type> copy () const
QMemArray<type> & assign ( const QMemArray<type> & a )
QMemArray<type> & assign ( const type * data, uint size )
QMemArray<type> & duplicate ( const QMemArray<type> & a )
QMemArray<type> & duplicate ( const type * data, uint size )
QMemArray<type> & setRawData ( const type * data, uint size )
void resetRawData ( const type * data, uint size )
int find ( const type & v, uint index = 0 ) const
int contains ( const type & v ) const
void sort ()
int bsearch ( const type & v ) const
type & operator[] ( int index ) const
type & at ( uint index ) const
operator const type * () const
bool operator== ( const QMemArray<type> & a ) const
bool operator!= ( const QMemArray<type> & a ) const
Iterator begin ()
Iterator end ()
ConstIterator begin () const
ConstIterator end () const

  Protected Members
QMemArray ( int, int )

RELATED FUNCTION DOCUMENTATION
Q_UINT16 qChecksum ( const char * data, uint len )
QDataStream & operator<< ( QDataStream & s, const QByteArray & a )
QDataStream & operator>> ( QDataStream & s, QByteArray & a )

DESCRIPTION
The QMemArray class is a template class that provides arrays of simple types.

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 deal only 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 collection classes, it has pointers to the contained items.

QMemArray uses explicit sharing with a reference count. If more than one array share common data and one array is modified, all arrays will be modified.

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

Example:

    #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 6 first 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;
    }

Program output:

    0: 1
    1: 1
    2: 2
    3: 3
    4: 5
    5: 8
    1 is found 2 times
    5 is found at index 4

Note about using 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:

    // 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

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.

See also Shared Classes and Non-GUI Classes.

  Member Type Documentation

QMemArray::ConstIterator
A const QMemArray iterator.

See also begin() and end().

QMemArray::Iterator
A QMemArray iterator.

See also begin() and end().

MEMBER FUNCTION DOCUMENTATION

QMemArray::QMemArray ( int, int ) [protected]
Constructs an array without allocating array space. The arguments should be (0, 0). Use at your own risk.

QMemArray::QMemArray ()
Constructs a null array.

See also isNull().

QMemArray::QMemArray ( int size )
Constructs an array with room for size elements. Makes a null array if size == 0.

The elements are left uninitialized.

See also resize() and isNull().

QMemArray::QMemArray ( const QMemArray<type> & a )
Constructs a shallow copy of a.

See also assign().

QMemArray::~QMemArray ()
Dereferences the array data and deletes it if this was the last reference.

QMemArray<type> & QMemArray::assign ( const QMemArray<type> & a )
Shallow copy. Dereferences the current array and references the data contained in a instead. Returns a reference to this array.

See also operator=().

QMemArray<type> & QMemArray::assign ( const type * data, uint size )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

Do not delete data later; QMemArray will take care of it.

type & QMemArray::at ( uint index ) const
Returns a reference to the element at position index in the array.

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

See also operator[]().

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. In fact, not only does it behave like a usual pointer, it is a pointer.

ConstIterator QMemArray::begin () const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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. In fact, not only does it behave like a usual pointer, it is a pointer.

int QMemArray::bsearch ( const type & v ) const
In a sorted array, finds the first occurrence of v by using binary search. For a sorted array this is generally much faster than find(), which does a linear search.

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

See also sort() and find().

int QMemArray::contains ( const type & v ) const
Returns the number of times v occurs in the array.

See also find().

QMemArray<type> QMemArray::copy () const
Returns a deep copy of this array.

See also detach() and duplicate().

uint QMemArray::count () const
Returns the same as size().

See also size().

Example: scribble/scribble.cpp.

type * QMemArray::data () const
Returns a pointer to the actual array data.

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

See also isNull().

Examples:

void QMemArray::detach () [virtual]
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 reference count is greater than one.

See also copy().

Reimplemented in QBitArray.

QMemArray<type> & QMemArray::duplicate ( const QMemArray<type> & a )
Deep copy. Dereferences the current array and obtains a copy of the data contained in a instead. Returns a reference to this array.

See also copy().

QMemArray<type> & QMemArray::duplicate ( const type * data, uint size )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

See also copy().

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. In fact, not only does it behave like a usual pointer, it is a pointer.

ConstIterator QMemArray::end () const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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. In fact, not only does it behave like a usual pointer, it is a pointer.

bool QMemArray::fill ( const type & v, int size = -1 )
Fills the array with the value v. If size is specified as different from -1, then the array will be resized before being filled.

Returns TRUE if successful, or FALSE if the memory cannot be allocated (only when size != -1).

See also resize().

int QMemArray::find ( const type & v, uint index = 0 ) const
Finds the first occurrence of v, starting at position index.

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

See also contains().

bool QMemArray::isEmpty () const
Returns TRUE if the array is empty; otherwise returns FALSE.

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

bool QMemArray::isNull () const
Returns TRUE if the array is null; otherwise returns FALSE.

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

uint QMemArray::nrefs () const
Returns the reference count for the shared array data. This reference count is always greater than zero.

QMemArray::operator const type * () const
Cast operator. Returns a pointer to the array.

See also data().

bool QMemArray::operator!= ( const QMemArray<type> & a ) const
Returns TRUE if this array is different from a; otherwise returns FALSE.

The two arrays are compared bitwise.

See also operator==().

QMemArray<type> & QMemArray::operator= ( const QMemArray<type> & a )
Assigns a shallow copy of a to this array and returns a reference to this array.

Equivalent to assign( a ).

bool QMemArray::operator== ( const QMemArray<type> & a ) const
Returns TRUE if this array is equal to a; otherwise returns FALSE.

The two arrays are compared bitwise.

See also operator!=().

type & QMemArray::operator[] ( int index ) const
Returns a reference to the element at position index in the array.

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

See also at().

void QMemArray::resetRawData ( const type * data, uint size )
Resets raw data that was set using setRawData().

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

See also setRawData().

bool QMemArray::resize ( uint size )
Resizes (expands or shrinks) the array to size elements. The array becomes a null array if size == 0.

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

New elements will not be initialized.

See also size().

Example: fileiconview/qfileiconview.cpp.

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 data and the new array size to size. Do not attempt to resize or re-assign the array data when raw data has been set. Call resetRawData(data, 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):

    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

Example II (you don't want to do this):

    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

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.

See also resetRawData().

uint QMemArray::size () const
Returns the size of the array (max number of elements).

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

See also isNull() and resize().

void QMemArray::sort ()
Sorts the array elements in ascending order, using bitwise comparison (memcmp()).

See also bsearch().

bool QMemArray::truncate ( uint pos )
Truncates the array at position pos.

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

Equivalent to resize(pos).

See also resize().

RELATED FUNCTION DOCUMENTATION

QDataStream & operator<< ( QDataStream & s, const QByteArray & a )
Writes byte array a to the stream s and returns a reference to the stream.

See also Format of the QDataStream operators.

QDataStream & operator>> ( QDataStream & s, QByteArray & a )
Reads a byte array into a from the stream s and returns a reference to the stream.

See also Format of the QDataStream operators.

Q_UINT16 qChecksum ( const char * data, uint len )
Returns the CRC-16 checksum of len bytes starting at data.

The checksum is independent of the byte order (endianness).

SEE ALSO
http://doc.trolltech.com/qmemarray.html http://www.trolltech.com/faq/tech.html

COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com. See the license file included in the distribution for a complete license statement.

AUTHOR
Generated automatically from the source code.

BUGS
If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports help us to help you. Thank you.

The definitive Qt documentation is provided in HTML format; it is located at $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.

If you find errors in this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qmemarray.3qt) and the Qt version (3.0.3).