On Wednesday, February 9, 2005 at 12:41:42 (-0500) Noah Schwartz writes:

...

... so youre saying that if i want to use boost i cant realistically use mak to compil my projects?

Not at all. Once boost is compiled and installed, make (etc.) works just fine. Bill

On Wed, 2005-02-09 at 20:02 -0700, Welson Sun wrote:

Hi,

I am new to C++ and I am converting a Java project to C++. Here is the error I got:

I believe I see your problem here. You want OperatorType to be a pure virtual class. Well you cannot use a class that has a pure virtual function you cannot create an object of that type. The purpose of a class with pure virtual functions is to be a base class like you are using with OperatorType. So we need to change your code ignore to make it say that OperatorType is a base class which BasicOperatorType inherits from: <BEFORE> class OperatorType { public: virtual string getMnemonic(void); }; <AFTER> class OperatorType { public: virtual string getMnemonic(void) = 0; }; Quote from: http://www.firststep.com.au/jlc/javacc/virtual.html While we're on the subject of virtual functions ... Java, like C++, supports pure virtual, or abstract, functions (Base class functions which must be defined in derived classes). In C++, the cryptic notation "=0" is used at the end of the function declaration. Java uses the more sensible abstract keyword. If your class has any abstract member functions, Java also insists that you declare the class as abstract. This advertises that it's an abstract class (In C++, you have to look through the member functions and notice that there's at least one pure virtual function). So we repeat this change for class Operator as well. So we are not done yet changing your code. We need to change the OperatorType and Operator declarations to be pointer types, e.g. OperatorType*. Since you cannot define a Operator type because a function is declared pure virtual you can still use it as a pointer. What you are saying is that the pointer is of type Operator but in fact is a class that supports the Operator interface. <BEFORE> // NOTE: This is what the class Operator would look like after making // the change described above. Its function getOperatorType is // now a pure virtual function which anything wanting to support // the Operator interface must define. class Operator{ public: virtual OperatorType getOperatorType() = 0; }; <AFTER> class Operator{ public: virtual OperatorType* getOperatorType() = 0; }; So anything wanting to support the Operator interface must have a function called getOperatorType that returns a pointer to a class which supports the OperatorType interface. Does that make sense? The final step after making these changes is to use these new classes. static OperatorType* portType = new BasicOperatorType("Port"); Here is a variable that is a OperatorType pointer called portType. Since BasicOperatorType supports the OperatorType we can assign a pointer on the heap of type BasicOperatorType to the portType variable. The only operations supported on portType is the getMnemonic() function. I would recommend two books: C++ Primer Plus - 4th Edition (or latest) from Stephen Prata. The C++ Programming Language (Special 3rd Edition) by Bjarne Stroustrup. I use the first one but a good friend of my likes the other. Both are good guides for getting into the C++ programming language. Cheers! Stephen

Hi, here is another problem I met: $ g++ main.cpp main.cpp: In member function `void schedule_vertex_writer<Graph>::operator()(std::ostream&, const Vertex&) const [with Vertex = unsigned int, Graph = boost::adjacency_list]': /usr/local/include/boost/graph/graphviz.hpp:264: instantiated from `void boost ::write_graphviz(std::ostream&, const Graph&, VertexPropertiesWriter, EdgeProper tiesWriter, GraphPropertiesWriter) [with Graph = boost::adjacency_list, VertexPropertiesWriter = schedule_vertex_writer >, EdgePropertiesWrite r = boost::default_writer, GraphPropertiesWriter = boost::default_writer]' /usr/local/include/boost/graph/graphviz.hpp:292: instantiated from `void boost ::write_graphviz(std::ostream&, const Graph&, VertexWriter) [with Graph = Graph, VertexWriter = schedule_vertex_writer >]' main.cpp:93: instantiated from here main.cpp:52: error: passing `const BasicOperator' as `this' argument of ` virtual OperatorType* BasicOperator::getOperatorType()' discards qualifiers The source code is in the attachment. Thanks!

On Feb 10, 2005, at 10:25 PM, Welson Sun wrote:

Well, I found out that this is not a problem related to inheritence nor polymorphism, it is a problem with the BGL

1. Even if I make BasicOperator not inherit from Operator, the problem is the same. Here is the modified BasicOperator:

class BasicOperator /* : public Operator */{ public: BasicOperator() {}; BasicOperator(OperatorType* type) : _type(type) {toString = _type->getMnemonic();}; BasicOperator(OperatorType* type, string cust) : _type(type), _cust(cust) {toString = _type->getMnemonic() + "&" + _cust;}; OperatorType* getOperatorType() { return _type; } string toString() { return toString; } string toString; private: OperatorType* _type; string _cust; };

And the vertex property writer is: void operator()(std::ostream& out, const Vertex& v) const { out << "[label=\"" << "(" << g[v].toString() << ")" << "\"]"; }

The error is: main.cpp:52: error: passing `const BasicOperator' as `this' argument of ` std::string BasicOperator::toString()' discards qualifiers

Looking at the code you previously posted and mapping that to what you've written here, here's what happens: schedule_vertex_writer stores a _copy_ of the graph (called g) inside it. Since operator() is marked "const", g[v] returns a reference to a const BasicOperator. But, when you call toString(), it is not marked const, so you get the error above. I have two suggestions: (1) Pass and store the graph g as a "const Graph&" in schedule_vertex_writer. Copying graphs can be really expensive. (2) Make toString() const. If you absolutely cannot do this, then you'll need to store a non-const reference to the graph instead of a const one.

So it looks like that the problem is related to the "const" BasicOperator I passed into std::string BasicOperator::toString(). How can I fix this? Which means if the property of a vertex is a Class, how can I call its member function in the vertex writer?

2. If I changes the vertex property writer as: void operator()(std::ostream& out, const Vertex& v) const { out << "[label=\"" << "(" << g[v].toString << ")" << "\"]"; } Everything is OK. Which mean in the vertex property writer, I can access the data member without any problem, but I cannot access the member function.

Right, because data members can be accessed irrespective of the cv-qualifiers on the object type. You'll just get a const std::string& back. Doug

Now another question arises: The vertex property writer is working, but if I add the edge property writer, it compiles error again: $ g++ main.cpp /usr/local/include/boost/graph/graphviz.hpp: In function `void boost::write_graphviz(std::ostream&, const Graph&, VertexPropertiesWriter, EdgePropertiesWriter, GraphPropertiesWriter) [with Graph = boost::adjacency_list, VertexPropertiesWriter = schedule_vertex_writer >, EdgePropertiesWriter = schedule_edge_writer >, GraphPropertiesWriter = boost::default_writer]': /usr/local/include/boost/graph/graphviz.hpp:300: instantiated from `void boos ::write_graphviz(std::ostream&, const Graph&, VertexWriter, EdgeWriter) [with G aph = Graph, VertexWriter = schedule_vertex_writer >, EdgeWriter = schedule_edge_writer >]' main.cpp:51: instantiated from here /usr/local/include/boost/graph/graphviz.hpp:270: error: no match for call to `( schedule_edge_writer >) (std::basic_ostream&, boost::detail::edge_desc_impl)' helper.hpp:73: error: candidates are: void schedule_edge_writer<Graph>::operator()(std::ostream&, Edge&) [with Edge = boost::detail::edge_desc_impl, Graph = boost::adjacency_list] I use the same pattern for vertex property writer and edge property writer, here is the code snapshot: //Class template of a vertex property writer template < typename Graph > class schedule_vertex_writer { public: schedule_vertex_writer(Graph _g) : g(_g) {} template <typename Vertex> void operator()(std::ostream& out, Vertex& v) { out << "[label=\"" << g[v].toString() << "\"]"; } private: Graph& g; }; //Function template to return an object of the above class template <typename Graph> inline schedule_vertex_writer<Graph> make_schedule_vertex_writer(Graph g){ return schedule_vertex_writer<Graph>(g); } //Class template of an edge property writer template < typename Graph > class schedule_edge_writer { public: schedule_edge_writer(Graph _g) : g(_g) {} template <typename Edge> void operator()(std::ostream& out, Edge& v) { out << "[label=\"" << "E" << "\"]"; } private: Graph& g; }; //Function template to return an object of the above class template <typename Graph> inline schedule_edge_writer<Graph> make_schedule_edge_writer(Graph g){ return schedule_edge_writer<Graph>(g); } -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Welson Sun Sent: Friday, February 11, 2005 3:19 PM To: boost-users@lists.boost.org Subject: RE: [Boost-users] BGL problem,originally [Another C++inheritence/polymorphism problem] Yeah, if I change the vertex property writer to be: void operator()(std::ostream& out, Vertex& v) It works fine. -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Douglas Gregor Sent: Friday, February 11, 2005 6:23 AM To: boost-users@lists.boost.org Subject: Re: [Boost-users] BGL problem,originally [Another C++ inheritence/polymorphism problem] On Feb 10, 2005, at 10:25 PM, Welson Sun wrote:

Well, I found out that this is not a problem related to inheritence nor polymorphism, it is a problem with the BGL

1. Even if I make BasicOperator not inherit from Operator, the problem is the same. Here is the modified BasicOperator:

class BasicOperator /* : public Operator */{ public: BasicOperator() {}; BasicOperator(OperatorType* type) : _type(type) {toString = _type->getMnemonic();}; BasicOperator(OperatorType* type, string cust) : _type(type), _cust(cust) {toString = _type->getMnemonic() + "&" + _cust;}; OperatorType* getOperatorType() { return _type; } string toString() { return toString; } string toString; private: OperatorType* _type; string _cust; };

And the vertex property writer is: void operator()(std::ostream& out, const Vertex& v) const { out << "[label=\"" << "(" << g[v].toString() << ")" << "\"]"; }

The error is: main.cpp:52: error: passing `const BasicOperator' as `this' argument of ` std::string BasicOperator::toString()' discards qualifiers

Looking at the code you previously posted and mapping that to what you've written here, here's what happens: schedule_vertex_writer stores a _copy_ of the graph (called g) inside it. Since operator() is marked "const", g[v] returns a reference to a const BasicOperator. But, when you call toString(), it is not marked const, so you get the error above. I have two suggestions: (1) Pass and store the graph g as a "const Graph&" in schedule_vertex_writer. Copying graphs can be really expensive. (2) Make toString() const. If you absolutely cannot do this, then you'll need to store a non-const reference to the graph instead of a const one.

So it looks like that the problem is related to the "const" BasicOperator I passed into std::string BasicOperator::toString(). How can I fix this? Which means if the property of a vertex is a Class, how can I call its member function in the vertex writer?

2. If I changes the vertex property writer as: void operator()(std::ostream& out, const Vertex& v) const { out << "[label=\"" << "(" << g[v].toString << ")" << "\"]"; } Everything is OK. Which mean in the vertex property writer, I can access the data member without any problem, but I cannot access the member function.

Right, because data members can be accessed irrespective of the cv-qualifiers on the object type. You'll just get a const std::string& back. Doug _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Thanks, you are right. Now both the vertex property writer and edge property writer works. But I don't understand why "reference" will cause this problem? Isn't it just an alias of an object? -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Douglas Gregor Sent: Friday, February 11, 2005 8:49 PM To: boost-users@lists.boost.org Subject: Re: [Boost-users] BGL problem,originally [Another C++inheritence/polymorphism problem] On Feb 11, 2005, at 6:00 PM, Welson Sun wrote:

template <typename Vertex> void operator()(std::ostream& out, Vertex& v) { out << "[label=\"" << g[v].toString() << "\"]"; [snip] template <typename Edge> void operator()(std::ostream& out, Edge& v) { out << "[label=\"" << "E" << "\"]"; }

I think it's a problem with the reference... typically, you just accept vertex and edge descriptors by-value (not by-reference), because they're small and cheap to copy. So the second operator() would start with: template<typename Edge> void operator()(std::ostream& out, Edge v) { Doug _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users