Specialization of template method - what's wrong with my code? - c++

Question

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 compile says
error: specialization of ‘size_t School::count() [with T = Boy]’
after instantiation
Could you please help?
ps. This is how I'm going to use it later:
School s;
size_t c = s.count<Boy>();

Answer 1

You are missing a semi-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();
}

Answer 2

Have you accidentally called count<Boy> in School before it is declared? 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 of count_boys() after all template members are specialized.

Answer 3

This compilable code compiles and runs OK 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 future, please make more effort to post compilable code - in other words, code with the necessary header files and supporting classes.