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Question

I am trying to cerate my own class with boost::adjacency_matrix graph as a member, but I am stuck on compilation error. Sample class that won't compile:

namespace zto {

typedef boost::adjacency_matrix<boost::undirectedS> Graph;

class SampleClass
{
public:
    Graph g;
    SampleClass();
};

And the compilation error:

./src/sample.cpp: In constructor ‘zto::SampleClass::SampleClass()’:
./src/sample.cpp:27:31: error: no matching function for call to 
  ‘boost::adjacency_matrix<boost::undirectedS>::adjacency_matrix()’
./src/sample.cpp:27:31: note: candidates are:
/usr/include/boost/graph/adjacency_matrix.hpp:622:5: note: template<class EdgeIterator, 
  class EdgePropertyIterator> boost::adjacency_matrix::adjacency_matrix(EdgeIterator, 
  EdgeIterator, EdgePropertyIterator, boost::adjacency_matrix<Directed, VertexProperty, 
  EdgeProperty, GraphProperty, Allocator>::vertices_size_type, const GraphProperty&)
/usr/include/boost/graph/adjacency_matrix.hpp:604:5: note: template<class EdgeIterator> 
  boost::adjacency_matrix::adjacency_matrix(EdgeIterator, EdgeIterator, 
  boost::adjacency_matrix<Directed, VertexProperty, EdgeProperty, GraphProperty, 
  Allocator>::vertices_size_type, const GraphProperty&)
/usr/include/boost/graph/adjacency_matrix.hpp:593:5: note: 
  boost::adjacency_matrix<Directed, VertexProperty, EdgeProperty, GraphProperty, 
  Allocator>::adjacency_matrix(boost::adjacency_matrix<Directed, VertexProperty, 
  EdgeProperty, GraphProperty, Allocator>::vertices_size_type, const GraphProperty&) 
  [with Directed = boost::undirectedS, VertexProperty = boost::no_property, EdgeProperty 
  = boost::no_property, GraphProperty = boost::no_property, Allocator = 
  std::allocator<bool>, boost::adjacency_matrix<Directed, VertexProperty, EdgeProperty, 
  GraphProperty, Allocator>::vertices_size_type = unsigned int]
/usr/include/boost/graph/adjacency_matrix.hpp:593:5: note:   candidate expects 2 
  arguments, 0 provided
/usr/include/boost/graph/adjacency_matrix.hpp:474:9: note: 
  boost::adjacency_matrix<boost::undirectedS>::adjacency_matrix(const 
  boost::adjacency_matrix<boost::undirectedS>&)
/usr/include/boost/graph/adjacency_matrix.hpp:474:9: note:   candidate expects 1 
  argument, 0 provided

It looks like that compilator thinks Graph is a function?!

Can anybody tell me, how to declare boost::adjacency_matrix as a member of my class?

Answer 1

The object member of your class is intitialized using a default constructor if you don't specify anything else as initializer. It seems that adjacency_matrix does not have a default constructor.

You should do something like this instead:

typedef boost::adjacency_matrix Graph;

class SampleClass
{
public:
    Graph g;
    SampleClass(size_t arg)
    : g(arg) // this is important
    {
      // As before, can also be in a cpp. 
      // It is just important that the initializer is used.
    }

};

Of course, in practice you could also make use of the other constructor arguments, use you won defaults, etc. This should just be a very simple example. I have never used boost::adjecency_matrix so I don't know about good practice and what actually makes sense. I just took this from the error message.

Answer 2

The compiler is telling you that boost::adjacency_matrix doesn't have a constructor taking no arguments, so it's unable to construct one as a member of your class. Object members of classes have to be constructed at the same time that the containing class is constructed, and unless you specify otherwise the compiler assumes there's a constructor with no parameters that it can call. When there isn't, you get errors like this.

The solution is to provide parameters for g's constructor in your constructor's initializer list:

SampleClass() : g( ... )
{
}

Where the ... is the appropriate constructor parameters for whatever one of adjacency_matrix's constructors gets you the object you want. This will override the compiler's default instinct to try to call the 0-parameter constructor, and make it call whichever one matches the parameters you supply instead.

If you don't want to do it at your class's construction time, you'll have to store a pointer to it and construct it using new at the appropriate time. Or better, store a shared_ptr to it so you don't have to worry about deleting it when your class is destroyed.

Answer 3

As far as I understand there is no default constructor for Graph.

You should provide a parameters, so just refer to documentation .