CODEWITHSUNDEEP
c++polymorphismvirtual
user3612348
user3612348

Reputation: 21

C++ Call virtual method of child class instead of base class

I have a base class Feature

feature.h

#ifndef FEATURE_H   
#define FEATURE_H

#include <string>
#include <map>

using namespace std;

template <class T> class Feature
{
public:
    virtual map<string, double> calculate(T input)
    {
        map<string, double> empty;

        return empty;
    }
};

#endif FEATURE_H

And a child class AvgSentenceLength

avgSentenceLength.h

#include "text.h"
#include "feature.h"

class AvgSentenceLength : public Feature<Text>
{
public:
    map<string, double> calculate(Text text);
};

I try to call calculate method from another file using AvgSentenceLength object, not directly but still:

map<int, Feature<Text>> features;
AvgSentenceLength avgSentenceLength;
features.insert(pair<int, Feature<Text>>(1, avgSentenceLength));

map<string, double> featuresValues;
featuresValues = features.at(1).calculate(text);

I want to call calculate method of the child class, but it calls calculate method of the base class. I can't use pure virtual function in the base class because it is necessary to create objects of this class.

Upvotes: 1

Views: 710

Answers (2)

Nassim
Nassim

Reputation: 301

simply add a pointer* to this line:map<int, Feature<Text>> features

so that its like this: map<int, Feature<Text>*> features.

Upvotes: 1

Ryan T. Grimm
Ryan T. Grimm

Reputation: 1325

You need to change map<int, Feature<Text>> to map<int, Feature<Text>*>. To Call polymorphic function through its base you need a level of indirection such as a pointer or a reference.

Upvotes: 4

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