compiling x and error in y templated inheritance

**noobcpp** · 10-19-2008

I've a class paramsMapCore

Code:

template <typename KeyType, typename ValueType>
class paramsMapCore : public std::map<KeyType, ValueType>{
  ...
}

and another Class paramsMap

Code:

class paramsMap : public paramsMapCore<string, Var>{
  ...
}

All these Classes compiles and works nice.

I just another Class Js::Object
Which is in Js namespace.

Code:

class Object: public Js::JVar, public paramsMapCore<string, Js::JVar>{
  ...
}

when it compiles object.cpp it doesn't fires any error on object.cpp or object.h
but it shows some error comming from paramsmap.h and paramsmap.hpp

wondering cause If I remove the Js::Object class everything including the paramsMap and paramsMapCore works fine.

This is the error message

Code:

compiling object.cpp (g++)
cgi++/paramsmap.h:36: error: expected template-name before '<' token
cgi++/paramsmap.h:36: error: expected `{' before '<' token
cgi++/paramsmap.h:36: error: expected unqualified-id before '<' token
cgi++/object.cpp:34: instantiated from here
cgi++/paramsmapcore.hpp:38: error: conversion from 'Var' to non-scalar type 'Js::JVar' requested

and another thing that makes me pull my hair is I've included paramsmapcore.h from object.h but I've never included paramsmap.h from object.h so why its bothering about paramsmap.h

Not getting any clue to solve plese help

**Elysia** · 10-19-2008

Not only moderators can help, you know...
Anyway, the thing is that templates are only parsed and evaluated once they're instantiated. If you don't instantiate them, the compiler will basically ignore them.
So you may "think" that your class is fine, but in reality it may be not.

**King Mir** · 10-19-2008

You can't inherent from std::map; it doesn't use virtual functions that are needed for inheritance. But thats not the cause of your errors.

**noobcpp** · 10-20-2008

So Whats the cause of the error ??

inheriting from std::map can be discussed in a separate topic

**noobcpp** · 10-20-2008

Here goes all my source codes with #include directivrs

object.h

Code:

#ifndef JSOBJECT_H
#define JSOBJECT_H

#include "jvar.h"
#include "paramsmapcore.h"
#include <sstream>
#include <string>

using std::string;
using std::stringstream;

namespace Js{

class Object: public Js::JVar, public paramsMapCore<string, Js::JVar>{
  public:
    Object();
    ~Object();
};

}

#endif

object.cpp

Code:

#include "object.h"

namespace Js {

Object::Object(): Js::JVar(), paramsMapCore<string, Js::JVar>(){

}


Object::~Object(){

}


}

paramsmapcore.h

Code:

#ifndef PARAMSMAPCORE_H
#define PARAMSMAPCORE_H

#include <map>
#include <string>
#include "var.h"

class Var;

template <typename KeyType, typename ValueType>
class paramsMapCore : public std::map<KeyType, ValueType>{
  public:
    paramsMapCore();
    ~paramsMapCore();
  public:
    bool exists(const KeyType& key) const;
    virtual ValueType get(const KeyType& key) const;
    virtual void set(const KeyType& key, const ValueType& val);
    bool remove(const KeyType& key);
    void removeAll();
    typename paramsMapCore<KeyType, ValueType>::iterator search(const KeyType& key);
    typename paramsMapCore<KeyType, ValueType>::const_iterator search(const KeyType& key) const;
    typename paramsMapCore<KeyType, ValueType>::iterator each();
    typename paramsMapCore<KeyType, ValueType>::const_iterator each() const;
};
#include "paramsmapcore.hpp"
#endif

paramsmap.h

Code:

#ifndef PARAMSMAP_H
#define PARAMSMAP_H

#include <string>
#include <map>
#include "var.h"
#include "paramsmapcore.h"

using std::string;
using std::map;

class Var;

class paramsMap : public paramsMapCore<string, Var>{
  public:
    paramsMap();
    ~paramsMap();
};

#endif

**laserlight** · 10-20-2008

It seems that the error lies in or is related to jvar.h, var.h and/or paramsmapcore.hpp. I commented out those #include lines and made Js::JVar an empty struct and there was no errors when compiling with the MinGW port of g++ 3.4.5. There were warnings related to having virtual functions with a non-virtual destructor (i.e., you should be declaring paramsMapCore's destructor virtual, and you should not be publicly deriving from std::map to begin with).

**noobcpp** · 10-20-2008

I dont find anything wrong in Js::JVar.

jvar.h

Code:

namespace Js {

class JVar{
  public:
    JVar();
    virtual ~JVar();
};

}

and this is jvar.cpp

Code:

namespace Js {

JVar::JVar(){

}


JVar::~JVar(){

}


}

**noobcpp** · 10-20-2008

stuck in this problem for several days nobody can help me ??
I am scared..

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