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/****************************************************************************
**
** QValueVector class documentation
**
** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved.
**
** This file is part of the Qt GUI Toolkit.
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** This file may be used under the terms of the GNU General
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/*****************************************************************************
QValueVector documentation
*****************************************************************************/
/*!
\class QValueVector qvaluevector.h
\brief The QValueVector class is a value-based template class that provides a dynamic array.
\ingroup qtl
\ingroup tools
\ingroup shared
\mainclass
\reentrant
QValueVector is a Qt implementation of an STL-like vector
container. It can be used in your application if the standard \c
vector is not available for your target platforms. QValueVector is
part of the \link qtl.html Qt Template Library\endlink.
QValueVector\<T\> defines a template instance to create a vector
of values that all have the class T. QValueVector does not store
pointers to the members of the vector; it holds a copy of every
member. QValueVector is said to be value based; in contrast,
QPtrList and QDict are pointer based.
QValueVector contains and manages a collection of objects of type
T and provides random access iterators that allow the contained
objects to be addressed. QValueVector owns the contained
elements. For more relaxed ownership semantics, see QPtrCollection
and friends, which are pointer-based containers.
QValueVector provides good performance if you append or remove
elements from the end of the vector. If you insert or remove
elements from anywhere but the end, performance is very bad. The
reason for this is that elements must to be copied into new
positions.
Some classes cannot be used within a QValueVector: for example,
all classes derived from QObject and thus all classes that
implement widgets. Only values can be used in a QValueVector. To
qualify as a value the class must provide:
\list
\i a copy constructor;
\i an assignment operator;
\i a default constructor, i.e., a constructor that does not take any arguments.
\endlist
Note that C++ defaults to field-by-field assignment operators and
copy constructors if no explicit version is supplied. In many
cases this is sufficient.
QValueVector uses an STL-like syntax to manipulate and address the
objects it contains. See \link qtl.html this document\endlink for
more information.
Example:
\code
#include <qvaluevector.h>
#include <qstring.h>
#include <stdio.h>
class Employee
{
public:
Employee(): s(0) {}
Employee( const QString& name, int salary )
: n( name ), s( salary )
{ }
QString name() const { return n; }
int salary() const { return s; }
void setSalary( int salary ) { s = salary; }
private:
QString n;
int s;
};
int main()
{
typedef QValueVector<Employee> EmployeeVector;
EmployeeVector vec( 3 ); // vector of 3 Employees
vec[0] = Employee( "Bill", 50000 );
vec[1] = Employee( "Steve", 80000 );
vec[2] = Employee( "Ron", 60000 );
Employee joe( "Joe", 50000 );
vec.push_back( joe ); // vector expands to accommodate 4 Employees
joe.setSalary( 70000 );
EmployeeVector::iterator it;
for( it = vec.begin(); it != vec.end(); ++it )
printf( "%s earns %d\n", (*it).name().latin1(), (*it).salary() );
return 0;
}
\endcode
Program output:
\code
Bill earns 50000
Steve earns 80000
Ron earns 60000
Joe earns 50000
\endcode
As you can see, the most recent change to Joe's salary did not
affect the value in the vector because the vector created a copy
of Joe's entry.
Many Qt functions return const value vectors; to iterate over
these you should make a copy and iterate over the copy.
There are several ways to find items in the vector. The begin()
and end() functions return iterators to the beginning and end of
the vector. The advantage of getting an iterator is that you can
move forward or backward from this position by
incrementing/decrementing the iterator. The iterator returned by
end() points to the element which is one past the last element in
the container. The past-the-end iterator is still associated with
the vector it belongs to, however it is \e not dereferenceable;
operator*() will not return a well-defined value. If the vector is
empty(), the iterator returned by begin() will equal the iterator
returned by end().
The fastest way to access an element of a vector is by using
operator[]. This function provides random access and will return
a reference to the element located at the specified index. Thus,
you can access every element directly, in constant time, providing
you know the location of the element. It is undefined to access
an element that does not exist (your application will probably
crash). For example:
\code
QValueVector<int> vec1; // an empty vector
vec1[10] = 4; // WARNING: undefined, probably a crash
QValueVector<QString> vec2(25); // initialize with 25 elements
vec2[10] = "Dave"; // OK
\endcode
Whenever inserting, removing or referencing elements in a vector,
always make sure you are referring to valid positions. For
example:
\code
void func( QValueVector<int>& vec )
{
if ( vec.size() > 10 ) {
vec[9] = 99; // OK
}
};
\endcode
The iterators provided by vector are random access iterators,
therefore you can use them with many generic algorithms, for
example, algorithms provided by the STL or the \link qtl.html
QTL\endlink.
Another way to find an element in the vector is by using the
std::find() or \link qtl.html#qFind qFind()\endlink algorithms.
For example:
\code
QValueVector<int> vec;
...
QValueVector<int>::const_iterator it = qFind( vec.begin(), vec.end(), 3 );
if ( it != vector.end() )
// 'it' points to the found element
\endcode
It is safe to have multiple iterators on the vector at the same
time. Since QValueVector manages memory dynamically, all iterators
can become invalid if a memory reallocation occurs. For example,
if some member of the vector is removed, iterators that point to
the removed element and to all following elements become
invalidated. Inserting into the middle of the vector will
invalidate all iterators. For convenience, the function back()
returns a reference to the last element in the vector, and front()
returns a reference to the first element. If the vector is
empty(), both back() and front() have undefined behavior (your
application will crash or do unpredictable things). Use back() and
front() with caution, for example:
\code
QValueVector<int> vec( 3 );
vec.push_back( 1 );
vec.push_back( 2 );
vec.push_back( 3 );
...
if ( !vec.empty() ) {
// OK: modify the first element
int& i = vec.front();
i = 18;
}
...
QValueVector<double> dvec;
double d = dvec.back(); // undefined behavior
\endcode
Because QValueVector manages memory dynamically, it is recommended
that you contruct a vector with an initial size. Inserting and
removing elements happens fastest when:
\list
\i Inserting or removing elements happens at the end() of the
vector;
\i The vector does not need to allocate additional memory.
\endlist
By creating a QValueVector with a sufficiently large initial size,
there will be less memory allocations. Do not use an initial size
that is too big, since it will still take time to construct all
the empty entries, and the extra space will be wasted if it is
never used.
Because QValueVector is value-based there is no need to be careful
about deleting elements in the vector. The vector holds its own
copies and will free them if the corresponding member or the
vector itself is deleted. You can force the vector to free all of
its items with clear().
QValueVector is shared implicitly, which means it can be copied in
constant time. If multiple QValueVector instances share the same
data and one needs to modify its contents, this modifying instance
makes a copy and modifies its private copy; it thus does not
affect the other instances. This is often called "copy on write".
If a QValueVector is being used in a multi-threaded program, you
must protect all access to the vector. See QMutex.
There are several ways to insert elements into the vector. The
push_back() function insert elements into the end of the vector,
and is usually fastest. The insert() function can be used to add
elements at specific positions within the vector.
Items can be also be removed from the vector in several ways.
There are several variants of the erase() function which removes a
specific element, or range of elements, from the vector.
Vectors can be also sorted with various STL algorithms , or it can
be sorted using the \link qtl.html Qt Template Library\endlink.
For example with qHeapSort():
Example:
\code
QValueVector<int> v( 4 );
v.push_back( 5 );
v.push_back( 8 );
v.push_back( 3 );
v.push_back( 4 );
qHeapSort( v );
\endcode
QValueVector stores its elements in contiguous memory. This means
that you can use a QValueVector in any situation that requires an
array.
*/
/*! \enum QValueVector::value_type
The type of the object stored in the vector. */
/*! \enum QValueVector::ValueType
The type of the object stored in the vector. */
/*! \enum QValueVector::pointer
The pointer to T type. */
/*! \enum QValueVector::const_pointer
The const pointer to T type. */
/*! \enum QValueVector::iterator
The vector's iterator type. */
/*! \enum QValueVector::const_iterator
The vector's const iterator type. */
/*! \enum QValueVector::Iterator
The vector's iterator type. */
/*! \enum QValueVector::ConstIterator
The vector's const iterator type. */
/*! \enum QValueVector::reference
The reference to T type. */
/*! \enum QValueVector::const_reference
The const reference to T type. */
/*! \enum QValueVector::size_type
An unsigned integral type, used to represent various sizes. */
/*! \enum QValueVector::difference_type
A signed integral type used to represent the distance between two iterators. */
/*!
\fn QValueVector::QValueVector()
Constructs an empty vector without any elements. To create a
vector which reserves an initial amount of space for elements, use
\c QValueVector(size_type n).
*/
/*!
\fn QValueVector::QValueVector( const QValueVector<T>& v )
Constructs a copy of \a v.
This operation costs O(1) time because QValueVector is implicitly
shared.
The first modification to the vector does takes O(n) time, because
the elements must be copied.
*/
/*!
\fn QValueVector::QValueVector( std::vector<T>& v )
Constructs a copy of \a v.
*/
/*!
\fn QValueVector::QValueVector( const std::vector<T>& v )
This operation costs O(n) time because \a v is copied.
*/
/*!
\fn QValueVector::QValueVector( size_type n, const T& val )
Constructs a vector with an initial size of \a n elements. Each
element is initialized with the value of \a val.
*/
/*!
\fn QValueVector::~QValueVector()
Destroys the vector, destroying all elements and freeing the
allocated memory. References to the values in the vector and all
iterators of this vector become invalidated. Note that it is
impossible for an iterator to check whether or not it is valid:
QValueVector is tuned for performance, not for error checking.
*/
/*!
\fn QValueVector<T>& QValueVector::operator=( const QValueVector<T>& v )
Assigns \a v to this vector and returns a reference to this vector.
All iterators of the current vector become invalidated by this
operation. The cost of such an assignment is O(1) since
QValueVector is implicitly shared.
*/
/*!
\fn QValueVector<T>& QValueVector::operator=( const std::vector<T>& v )
\overload
Assigns \a v to this vector and returns a reference to this vector.
All iterators of the current vector become invalidated by this
operation. The cost of this assignment is O(n) since \a v is
copied.
*/
/*!
\fn size_type QValueVector::size() const
Returns the number of elements in the vector.
This function is provided for STL compatibility. It is equivalent
to count().
\sa empty()
*/
/*!
\fn size_type QValueVector::count() const
Returns the number of items in the vector.
\sa isEmpty()
*/
/*!
\fn bool QValueVector::empty() const
Returns TRUE if the vector is empty; otherwise returns FALSE.
Equivalent to size()==0, only faster.
This function is provided for STL compatibility. It is equivalent
to isEmpty().
\sa size()
*/
/*!
\fn bool QValueVector::isEmpty() const
Returns TRUE if the vector is empty; returns FALSE otherwise.
\sa count()
*/
/*!
\fn size_type QValueVector::capacity() const
Returns the maximum number of elements that can be stored in the
vector without forcing memory reallocation. If memory reallocation
takes place, some or all iterators may become invalidated.
*/
/*!
\fn iterator QValueVector::begin()
Returns an iterator pointing to the beginning of the vector. If
the vector is empty(), the returned iterator will equal end().
*/
/*!
\fn const_iterator QValueVector::begin() const
\overload
Returns a const iterator pointing to the beginning of the vector.
If the vector is empty(), the returned iterator will equal end().
*/
/*!
\fn const_iterator QValueVector::constBegin() const
Returns a const iterator pointing to the beginning of the vector.
If the vector is empty(), the returned iterator will equal end().
\sa constEnd();
*/
/*!
\fn iterator QValueVector::end()
Returns an iterator pointing behind the last element of the
vector.
*/
/*!
\fn const_iterator QValueVector::end() const
\overload
Returns a const iterator pointing behind the last element of the
vector.
*/
/*!
\fn const_iterator QValueVector::constEnd() const
Returns a const iterator pointing behind the last element of the
vector.
\sa constBegin()
*/
/*!
\fn reference QValueVector::at( size_type i , bool* ok )
Returns a reference to the element with index \a i. If \a ok is
non-null, and the index \a i is out of range, *\a ok is set to
FALSE and the returned reference is undefined. If the index \a i
is within the range of the vector, and \a ok is non-null, *\a ok
is set to TRUE and the returned reference is well defined.
*/
/*!
\fn const_reference QValueVector::at( size_type i , bool* ok ) const
\overload
Returns a const reference to the element with index \a i. If \a ok
is non-null, and the index \a i is out of range, *\a ok is set to
FALSE and the returned reference is undefined. If the index \a i
is within the range of the vector, and \a ok is non-null, *\a ok
is set to TRUE and the returned reference is well defined.
*/
/*!
\fn reference QValueVector::operator[]( size_type i )
Returns a reference to the element at index \a i. If \a i is out
of range, this function has undefined behavior.
\sa at()
*/
/*!
\fn const_reference QValueVector::operator[]( size_type i ) const
\overload
Returns a const reference to the element at index \a i. If \a i is
out of range, this function has undefined behavior.
\sa at()
*/
/*!
\fn reference QValueVector::front()
Returns a reference to the first element in the vector. If there
is no first element, this function has undefined behavior.
\sa empty() back()
*/
/*!
\fn const_reference QValueVector::front() const
\overload
Returns a const reference to the first element in the vector. If
there is no first element, this function has undefined behavior.
\sa empty() back()
*/
/*!
\fn reference QValueVector::first()
Returns a reference to the first item in the vector. If there is
no first item, this function has undefined behavior.
\sa empty() last()
*/
/*!
\fn const_reference QValueVector::first() const
\overload
*/
/*!
\fn reference QValueVector::back()
Returns a reference to the last element in the vector. If there is
no last element, this function has undefined behavior.
\sa empty() front()
*/
/*!
\fn const_reference QValueVector::back() const
\overload
Returns a const reference to the last element in the vector. If
there is no last element, this function has undefined behavior.
\sa empty() front()
*/
/*!
\fn reference QValueVector::last()
Returns a reference to the last item in the vector. If there is no
last item, this function has undefined behavior.
\sa empty() first()
*/
/*!
\fn const_reference QValueVector::last() const
\overload
*/
/*!
\fn void QValueVector::push_back( const T& x )
Appends a copy of \a x to the end of the vector. This is the
fastest way to add new elements.
This function is provided for STL compatibility. It is equivalent
to append().
\sa insert()
*/
/*!
\fn void QValueVector::append( const T& x )
Appends a copy of \a x to the end of the vector.
\sa push_back() insert()
*/
/*!
\fn void QValueVector::pop_back()
Removes the last item from the vector.
This function is provided for STL compatibility.
*/
/*!
\fn iterator QValueVector::insert( iterator pos, const T& x )
Inserts a copy of \a x at the position immediately before \a pos.
\sa push_back()
*/
/*! \fn void QValueVector::detachInternal()
\internal
*/
/*!
\fn iterator QValueVector::insert( iterator pos, size_type n, const T& x )
\overload
Inserts \a n copies of \a x immediately before position x.
\sa push_back()
*/
/*!
\fn void QValueVector::reserve( size_type n )
Increases the vector's capacity. If \a n is less than or equal to
capacity(), nothing happens. Otherwise, additional memory is
allocated so that capacity() will be increased to a value greater
than or equal to \a n. All iterators will then become invalidated.
Note that the vector's size() and the values of existing elements
remain unchanged.
*/
/*!
\fn void QValueVector::resize( size_type n, const T& val = T() )
Changes the size of the vector to \a n. If \a n is greater than
the current size(), elements are added to the end and initialized
with the value of \a val. If \a n is less than size(), elements
are removed from the end. If \a n is equal to size() nothing
happens.
*/
/*!
\fn void QValueVector::clear()
Removes all the elements from the vector.
*/
/*!
\fn iterator QValueVector::erase( iterator pos )
Removes the element at position \a pos and returns the position of
the next element.
*/
/*!
\fn iterator QValueVector::erase( iterator first, iterator last )
\overload
Removes all elements from \a first up to but not including \a last
and returns the position of the next element.
*/
/*!
\fn bool QValueVector::operator==( const QValueVector<T>& x ) const
Returns TRUE if each element in this vector equals each
corresponding element in \a x; otherwise returns FALSE.
*/
/*!
\fn bool QValueVector::operator==( const QValueVector<T>& x )
\overload
Returns TRUE if each element in this vector equals each
corresponding element in \a x; otherwise returns FALSE.
*/
/*!
\fn void QValueVector::detach()
\internal
If the vector does not share its data with another QValueVector
instance, nothing happens. Otherwise the function creates a new
copy of this data and detaches from the shared one. This function
is called whenever the vector is modified. The implicit sharing
mechanism is implemented this way.
*/