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Template method specialization - what happened to my code?

What's wrong with this code?

class School {
public:
    template<typename T> size_t count() const;
private:
    vector<Boy*> boys;
    vector<Girl*> girls;
};
template<> size_t School::count<Boy>() const {
    return boys.size();
}

My compiler says

error: specialization of ‘size_t School::count() [with T = Boy]’
after instantiation

Could you help me?

ps. This is how I will use it later:

School s;
size_t c = s.count<Boy>();
+2


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3 answers


Did you accidentally call count<Boy>

in School

before his announcement? One way to reproduce your error is

class Boy;
class Girl;

class School {
public:
    template<typename T> size_t count() const;
    size_t count_boys() const { return count<Boy>(); }
    // ^--- instantiation
private:
    std::vector<Boy*> boys;
    std::vector<Girl*> girls;
};

template<> size_t School::count<Boy>() const { return boys.size(); }
// ^--- specialization

int main () { School g; return 0; }


You need to move the definition count_boys()

after all members of the template are specialized.

+4


a source


You are missing a colon.



class School {
public:
    template<typename T> size_t count() const;
private:
    vector<Boy*> boys;
    vector<Girl*> girls;
};                           // <-- Missing semi-colon
template<> size_t School::count<Boy>() const {
    return boys.size();
}
+6


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This compiled code is compiled and run with g ++:

#include <vector>
using namespace std;

struct Boy {};
struct Girl {};

class School {
public:
    template<typename T> size_t count() const;
private:
    vector<Boy*> boys;
    vector<Girl*> girls;
};

template<> size_t School::count<Boy>() const {
    return boys.size();
}

int main() {
    School s;
    size_t c = s.count<Boy>();
}

In the future, please put more effort into posting compiled code - in other words, code with the required header files and supporting classes.

0


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