template<typename T, typename IndexMap = identity_property_map>
class vector_property_map;

This property map is used to efficiently store properties for a variable number of elements. It's somewhere between associative_property_map and iterator_property_map. The latter is very fast, but requires that the number of stored elements is known when creating property map. The former does not have this requirement, but is slower, and requires stored elements to be comparable.

The vector_property_map uses mapping from key to indices, and allows to add new elements. It accomplishes this by storing values in a vector, which is resized on demand.

Note that vector_property_map does not provide reference/pointer stability for stored values.

Example

#include <boost/property_map/vector_property_map.hpp>
#include <string>
#include <iostream>

int main()
{
    boost::vector_property_map<std::string> m;
    
    // Assign string to '4'. 
    m[4] = "e";
    std::cout << "'" << m[4] << "'\n";
    
    // Grab string from '10'. Since none is associated,
    // "" will be returned.
    std::cout << "'" << m[10] << "'\n";
}

Where Defined

boost/property_map/vector_property_map.hpp

Model Of

Template Parameters

Parameter	Description	Default
T	The type of property value. Must be both Assignable and DefaultConstructible.
IndexMap	Must be a model of Readable Property Map and the value type must be convertible to std::vector<T>::size_type.	identity_property_map

Members

In addition to the methods and functions required by Lvalue Property Map, this class has the following members.

vector_property_map(const IndexMap& index = IndexMap())

vector_property_map(unsigned initial_size, const IndexMap& index = IndexMap())

vector_property_map(const vector_property_map&)

vector_property_map& operator=(const vector_property_map&)

reference operator[](const key_type& v) const

std::vector<T>::iterator storage_begin()
std::vector<T>::iterator storage_end()
std::vector<T>::const_iterator storage_begin()
std::vector<T>::const_iterator storage_end()

This group of methods gives access to begin and end iterators of the underlying vector.

Rationale: The methods are handy, for example, when it's needed to specify a single value for all elements in a freshly created property map. The methods are not called simply "begin" and "end" since conceptually, vector_property_map is unbounded map, and has no end iterator. The direct access to the underlying method is not provided, since it would decrease encapsulation and make future performance tuning dangerous.

Acknolegements: Matthias Troyer suggested adding those functions.

void reserve(unsigned size)

Non-Member functions

template
vector_property_map
make_vector_property_map(IndexMap index)
{
  return vector_property_map(index);
}