QValueVector(3qt)QValueVector(3qt)NAMEQValueVector - Value-based template class that provides a dynamic array
SYNOPSIS
All the functions in this class are reentrant when Qt is built with
thread support.</p>
#include <qvaluevector.h>
Public Members
typedef T value_type
typedef value_type * pointer
typedef const value_type * const_pointer
typedef value_type * iterator
typedef const value_type * const_iterator
typedef value_type & reference
typedef const value_type & const_reference
typedef size_t size_type
typedef ptrdiff_t difference_type
QValueVector ()
QValueVector ( const QValueVector<T> & v )
QValueVector ( size_type n, const T & val = T ( ) )
QValueVector ( std::vector<T> & v )
QValueVector ( const std::vector<T> & v )
~QValueVector ()
QValueVector<T> & operator= ( const QValueVector<T> & v )
QValueVector<T> & operator= ( const std::vector<T> & v )
size_type size () const
bool empty () const
size_type capacity () const
iterator begin ()
const_iterator begin () const
const_iterator constBegin () const
iterator end ()
const_iterator end () const
const_iterator constEnd () const
reference at ( size_type i, bool * ok = 0 )
const_reference at ( size_type i, bool * ok = 0 ) const
reference operator[] ( size_type i )
const_reference operator[] ( size_type i ) const
reference front ()
const_reference front () const
reference back ()
const_reference back () const
void push_back ( const T & x )
void pop_back ()
iterator insert ( iterator pos, const T & x )
iterator insert ( iterator pos, size_type n, const T & x )
void reserve ( size_type n )
void resize ( size_type n, const T & val = T ( ) )
void clear ()
iterator erase ( iterator pos )
iterator erase ( iterator first, iterator last )
bool operator== ( const QValueVector<T> & x )
bool operator== ( const QValueVector<T> & x ) const
typedef T ValueType
typedef ValueType * Iterator
typedef const ValueType * ConstIterator
size_type count () const
bool isEmpty () const
reference first ()
const_reference first () const
reference last ()
const_reference last () const
void append ( const T & x )
DESCRIPTION
The QValueVector class is a value-based template class that provides a
dynamic array.
QValueVector is a Qt implementation of an STL-like vector container. It
can be used in your application if the standard vector is not available
for your target platforms. QValueVector is part of the Qt Template
Library.
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:
a copy constructor;
an assignment operator;
a default constructor, i.e., a constructor that does not take any
arguments.
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 this document for more information.
Example:
#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;
}
Program output:
Bill earns 50000
Steve earns 80000
Ron earns 60000
Joe earns 50000
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 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:
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
Whenever inserting, removing or referencing elements in a vector,
always make sure you are referring to valid positions. For example:
void func( QValueVector<int>& vec )
{
if ( vec.size() > 10 ) {
vec[9] = 99; // OK
}
};
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 QTL.
Another way to find an element in the vector is by using the
std::find() or qFind() algorithms. For example:
QValueVector<int> vec;
...
QValueVector<int>::const_iterator it = qFind( vec.begin(), vec.end(), 3 );
if ( it != vector.end() )
// 'it' points to the found element
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:
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
Because QValueVector manages memory dynamically, it is recommended that
you contruct a vector with an initial size. Inserting and removing
elements happens fastest when:
Inserting or removing elements happens at the end() of the vector;
The vector does not need to allocate additional memory.
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 Qt Template Library. For example with qHeapSort():
Example:
QValueVector<int> v( 4 );
v.push_back( 5 );
v.push_back( 8 );
v.push_back( 3 );
v.push_back( 4 );
qHeapSort( v );
QValueVector stores its elements in contiguous memory. This means that
you can use a QValueVector in any situation that requires an array.
See also Qt Template Library Classes, Implicitly and Explicitly Shared
Classes, and Non-GUI Classes.
Member Type Documentation
QValueVector::ConstIterator
The vector's const iterator type.
QValueVector::Iterator
The vector's iterator type.
QValueVector::ValueType
The type of the object stored in the vector.
QValueVector::const_iterator
The vector's const iterator type.
QValueVector::const_pointer
The const pointer to T type.
QValueVector::const_reference
The const reference to T type.
QValueVector::difference_type
A signed integral type used to represent the distance between two
iterators.
QValueVector::iterator
The vector's iterator type.
QValueVector::pointer
The pointer to T type.
QValueVector::reference
The reference to T type.
QValueVector::size_type
An unsigned integral type, used to represent various sizes.
QValueVector::value_type
The type of the object stored in the vector.
MEMBER FUNCTION DOCUMENTATIONQValueVector::QValueVector ()
Constructs an empty vector without any elements. To create a vector
which reserves an initial amount of space for elements, use
QValueVector(size_type n).
QValueVector::QValueVector ( const QValueVector<T> & v )
Constructs a copy of 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.
QValueVector::QValueVector ( size_type n, const T & val = T ( ) )
Constructs a vector with an initial size of n elements. Each element is
initialized with the value of val.
QValueVector::QValueVector ( std::vector<T> & v )
Constructs a copy of v.
QValueVector::QValueVector ( const std::vector<T> & v )
This operation costs O(n) time because v is copied.
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.
void QValueVector::append ( const T & x )
Appends a copy of x to the end of the vector.
See also push_back() and insert().
reference QValueVector::at ( size_type i, bool * ok = 0 )
Returns a reference to the element with index i. If ok is non-null, and
the index i is out of range, *ok is set to FALSE and the returned
reference is undefined. If the index i is within the range of the
vector, and ok is non-null, *ok is set to TRUE and the returned
reference is well defined.
const_reference QValueVector::at ( size_type i, bool * ok = 0 ) const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns a const reference to the element with index i. If ok is non-
null, and the index i is out of range, *ok is set to FALSE and the
returned reference is undefined. If the index i is within the range of
the vector, and ok is non-null, *ok is set to TRUE and the returned
reference is well defined.
reference QValueVector::back ()
Returns a reference to the last element in the vector. If there is no
last element, this function has undefined behavior.
See also empty() and front().
const_reference QValueVector::back () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns a const reference to the last element in the vector. If there
is no last element, this function has undefined behavior.
See also empty() and front().
iterator QValueVector::begin ()
Returns an iterator pointing to the beginning of the vector. If the
vector is empty(), the returned iterator will equal end().
const_iterator QValueVector::begin () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns a const iterator pointing to the beginning of the vector. If
the vector is empty(), the returned iterator will equal end().
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.
void QValueVector::clear ()
Removes all the elements from the vector.
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().
See also constEnd().
const_iterator QValueVector::constEnd () const
Returns a const iterator pointing behind the last element of the
vector.
See also constBegin().
size_type QValueVector::count () const
Returns the number of items in the vector.
See also isEmpty().
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().
See also size().
iterator QValueVector::end ()
Returns an iterator pointing behind the last element of the vector.
const_iterator QValueVector::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 the
vector.
iterator QValueVector::erase ( iterator pos )
Removes the element at position pos and returns the position of the
next element.
iterator QValueVector::erase ( iterator first, iterator last )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Removes all elements from first up to but not including last and
returns the position of the next element.
reference QValueVector::first ()
Returns a reference to the first item in the vector. If there is no
first item, this function has undefined behavior.
See also empty() and last().
const_reference QValueVector::first () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
reference QValueVector::front ()
Returns a reference to the first element in the vector. If there is no
first element, this function has undefined behavior.
See also empty() and back().
const_reference QValueVector::front () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns a const reference to the first element in the vector. If there
is no first element, this function has undefined behavior.
See also empty() and back().
iterator QValueVector::insert ( iterator pos, const T & x )
Inserts a copy of x at the position immediately before pos.
See also push_back().
iterator QValueVector::insert ( iterator pos, size_type n, const T & x )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Inserts n copies of x immediately before position x.
See also push_back().
bool QValueVector::isEmpty () const
Returns TRUE if the vector is empty; returns FALSE otherwise.
See also count().
reference QValueVector::last ()
Returns a reference to the last item in the vector. If there is no last
item, this function has undefined behavior.
See also empty() and first().
const_reference QValueVector::last () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
QValueVector<T> & QValueVector::operator= ( const QValueVector<T> & v )
Assigns 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.
QValueVector<T> & QValueVector::operator= ( const std::vector<T> & v )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Assigns 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 v is copied.
bool QValueVector::operator== ( const QValueVector<T> & x ) const
Returns TRUE if each element in this vector equals each corresponding
element in x; otherwise returns FALSE.
bool QValueVector::operator== ( const QValueVector<T> & x )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns TRUE if each element in this vector equals each corresponding
element in x; otherwise returns FALSE.
reference QValueVector::operator[] ( size_type i )
Returns a reference to the element at index i. If i is out of range,
this function has undefined behavior.
See also at().
const_reference QValueVector::operator[] ( size_type i ) const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns a const reference to the element at index i. If i is out of
range, this function has undefined behavior.
See also at().
void QValueVector::pop_back ()
Removes the last item from the vector.
This function is provided for STL compatibility.
void QValueVector::push_back ( const T & x )
Appends a copy of 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().
See also insert().
void QValueVector::reserve ( size_type n )
Increases the vector's capacity. If 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 n. All iterators will then become invalidated. Note that the
vector's size() and the values of existing elements remain unchanged.
void QValueVector::resize ( size_type n, const T & val = T ( ) )
Changes the size of the vector to n. If n is greater than the current
size(), elements are added to the end and initialized with the value of
val. If n is less than size(), elements are removed from the end. If n
is equal to size() nothing happens.
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().
See also empty().
SEE ALSO
http://doc.trolltech.com/qvaluevector.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
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Trolltech AS 2 February 2007 QValueVector(3qt)