C++: Inserting pairs of class objects into a map - c++

Question

I am trying to insert into a map that contains a class name_t object as the key and a class scores_t object as the value. The name_t object should be a string, while the scores_t object is a vector of ints. I am getting errors when trying to do:
map.insert(std::pair<string, vector<int> >(n.get(), s.get()));
The program code is:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>
#include <map>
#include <functional>
#include <algorithm>
#include <numeric>
#include <iomanip>
using namespace std;
class name_t{
public:
void print_name(int);
bool operator<(const name_t &rhs) const;
void set(string first, string last);
string get() const { return name; }
//Add get/set functions for firstname and lastname
private:
string name;
string firstname;
string lastname;
};
void name_t::print_name(int n){
cout << left << setw(21) << setfill('.') << name << " ";
}
bool name_t::operator<(const name_t &rhs) const{
if(get()!=rhs.get()) return get() < rhs.get();
return false;
}
void name_t::set(string first, string last){
firstname = first;
lastname = last;
name = lastname + ", " + firstname;
}
class scores_t{
public:
void push_back(int);
void compute_stats();
void print_scores();
vector<int> get(){ return scores; }
//Add accessor functions for min, max, avg, n80
private:
vector<int> scores;
int min;
int max;
int avg, n80;
};
void scores_t::push_back(int num){
scores.push_back(num);
}
void scores_t::compute_stats(){
vector<int>::iterator it;
it = min_element(scores.begin(), scores.end());
min = *it;
it = max_element(scores.begin(), scores.end());
max = *it;
int init = 0;
avg = accumulate(scores.begin(), scores.end(), init)/scores.size();
n80 = count_if(scores.begin(), scores.end(), bind2nd(greater<int>(),80));
}
void scores_t::print_scores(){
cout << min << " " << max << " " << avg << " " << n80;
scores.clear();
}
int main(int argc, char* argv[]){
name_t n;
scores_t s;
ifstream fin;
string first, last;
int num, size, bsize=0;
string text;
map<name_t, scores_t> map;
fin.open(argv[1]);
while(getline(fin, text)){
stringstream ss(text);
while(ss >> first >> last){
n.set(first, last);
size = first.size() + last.size();
if(size > bsize){
bsize = size;
}
n.print_name(bsize);
while(ss >> num){
cout << num << " ";
s.push_back(num);
}
cout << ": ";
s.compute_stats();
map.insert(std::pair<string, vector<int> >(n.get(), s.get()));
s.print_scores();
}
cout << endl;
}
fin.close();
return 0;
}
I am getting these errors:
In file included from /usr/include/c++/4.8.2/bits/stl_algobase.h:64:0,
from /usr/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/include/c++/4.8.2/ios:40,
from /usr/include/c++/4.8.2/ostream:38,
from /usr/include/c++/4.8.2/iostream:39,
from Labstats1.cpp:1:
/usr/include/c++/4.8.2/bits/stl_pair.h: In instantiation of ‘std::pair<_T1, _T2>::pair(const std::pair<_U1, _U2>&) [with _U1 = std::basic_string<char>; _U2 = std::vector<int>; _T1 = const name_t; _T2 = scores_t]’:
Labstats1.cpp:106:64: required from here
/usr/include/c++/4.8.2/bits/stl_pair.h:119:39: error: no matching function for call to ‘name_t::name_t(const std::basic_string<char>&)’
: first(__p.first), second(__p.second) { }
^
/usr/include/c++/4.8.2/bits/stl_pair.h:119:39: note: candidates are:
Labstats1.cpp:13:7: note: name_t::name_t()
class name_t{
^
Labstats1.cpp:13:7: note: candidate expects 0 arguments, 1 provided
Labstats1.cpp:13:7: note: name_t::name_t(const name_t&)
Labstats1.cpp:13:7: note: no known conversion for argument 1 from ‘const std::basic_string<char>’ to ‘const name_t&’
In file included from /usr/include/c++/4.8.2/bits/stl_algobase.h:64:0,
from /usr/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/include/c++/4.8.2/ios:40,
from /usr/include/c++/4.8.2/ostream:38,
from /usr/include/c++/4.8.2/iostream:39,
from Labstats1.cpp:1:
/usr/include/c++/4.8.2/bits/stl_pair.h:119:39: error: no matching function for call to ‘scores_t::scores_t(const std::vector<int>&)’
: first(__p.first), second(__p.second) { }
^
/usr/include/c++/4.8.2/bits/stl_pair.h:119:39: note: candidates are:
Labstats1.cpp:43:7: note: scores_t::scores_t()
class scores_t{
^
Labstats1.cpp:43:7: note: candidate expects 0 arguments, 1 provided
Labstats1.cpp:43:7: note: scores_t::scores_t(const scores_t&)
Labstats1.cpp:43:7: note: no known conversion for argument 1 from ‘const std::vector<int>’ to ‘const scores_t&’
I'm not too sure what these errors mean. Any help is appreciated. Thank you!

Answer 1

Your map data type is std::pair<name_t, scores_t>, but you are trying to insert a pair of a std::string and std::vector - since this is what your get() functions are returning.
To solve the immediate compilation error, just use correct data type in insertion.
However, there are other, more subtle issues with your code. For instance, your get() functions return members by value. This means, that a copy will be made every time the function is called - and it takes quite a bite of time to copy the vector or string. Instead, you should expose your members through a function returning const reference.
Also, it is a good practice for a wrapper class (your classes are essentially wrappers) to define constructor which would take an argument of the wrapped type. For instance, for your name_t you might want a constructor like following:
name_t::name_t(const std::string& name) : name(name) {}