c++ - vector 排序中 C++ 模板函数出错

Question

我想使用模板函数对类的 vector 进行排序，但出现编译错误。错误是由于模板。当我使用类而不是模板时它会编译。

class Person
{
    private:
      int ssn;
      string name;

    public:
      Person() {};
      Person(int s, string na) { ssn = s; name = na; }
      const int getSSN() { return ssn; }

      friend ostream& operator <<(ostream& out, const Person& per) {
          out << per.ssn << "  " << per.name;
      }
};

template <typename T> 
bool myfunction(T i, T j) { return (i.getSSN() < j.getSSN()); }
// it complies fine when I use 
// bool myfunction(Person i, Person j) { return (i.getSSN() < j.getSSN()); }

int main()
{
    ifstream in("personal.dat");
    string st;
    vector<Person> *vect = new vector<Person>;
    int ssn;
    string name;
    while(in >> ssn >> name) {
            Person per(ssn, name);
            vect->push_back(per);
    }
    in.close();

    sort(vect->begin(), vect->end(), myfunction);
    for(int i=0; i<vect->size(); i++) cout << vect->at(i) << endl;
}

编译错误:

read.cxx: In function ‘int main()’:
read.cxx:41:45: error: no matching function for call to  ‘sort(std::vector<Person>::
iterator, std::vector<Person>::iterator, <unresolved overloaded function type>)’
sort(vect->begin(), vect->end(), myfunction);

read.cxx:41:45: note: candidates are:
In file included from /usr/include/c++/4.8.3/algorithm:62:0,
         from read.cxx:6:
/usr/include/c++/4.8.3/bits/stl_algo.h:5438:5: note: template<class _RAIter> 
void std::sort(_RAIter, _RAIter) sort(_RandomAccessIterator __first,
_RandomAccessIterator __last)
.................
.................

有什么建议吗？非常感谢。

Answer 1

你应该告诉它你想要比较的元素类型:

sort(begin, end, myfunction<Person>);