Boost C++ Libraries

Checks if a geometry is the empty set.

Synopsis

template<typename Geometry>
bool is_empty(Geometry const & geometry)

Parameters

Returns

Returns true if the geometry is the empty set

Header

Either

#include <boost/geometry.hpp>

Or

#include <boost/geometry/algorithms/is_empty.hpp>

Conformance

The function is_empty implements function IsEmpty from the OGC Simple Feature Specification.

Supported geometries

Complexity

Constant-time

Example

Check if a geometry is the empty set

#include <iostream>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>


int main()
{
    boost::geometry::model::multi_linestring
        <
            boost::geometry::model::linestring
                <
                    boost::geometry::model::d2::point_xy<double>
                >
        > mls;
    boost::geometry::read_wkt("MULTILINESTRING((0 0,0 10,10 0),(1 1,8 1,1 8))", mls);
    std::cout << "Is empty? " << (boost::geometry::is_empty(mls) ? "yes" : "no") << std::endl;
    boost::geometry::clear(mls);
    std::cout << "Is empty (after clearing)? " << (boost::geometry::is_empty(mls) ? "yes" : "no") << std::endl;
    return 0;
}

Output:

Is empty? no
Is empty (after clearing)? yes

See also