Question

This program has the user input name/age pairs and then outputs them, using a class. Here is the code.

#include "std_lib_facilities.h"

class Name_pairs
{
public:
       bool test();
       void read_names();
       void read_ages();
       void print();
private:
        vector<string>names;
        vector<double>ages;
        string name;
        double age;
};

void Name_pairs::read_names()
{
     cout << "Enter name: ";
     cin >> name;
     names.push_back(name);
     cout << endl;
}

void Name_pairs::read_ages()
{
     cout << "Enter corresponding age: ";
     cin >> age;
     ages.push_back(age);
     cout << endl;
}

void Name_pairs::print()
{
     for(int i = 0; i < names.size() && i < ages.size(); ++i)
             cout << names[i] << " , " << ages[i] << endl;
}

bool Name_pairs::test()
{
   int i = 0;
   if(ages[i] == 0 || names[i] == "0") return false;
   else{
        ++i;
        return true;}
}


int main()
{
    cout << "Enter names and ages. Use 0 to cancel.\n";
    while(Name_pairs::test())
    {
     Name_pairs::read_names();
     Name_pairs::read_ages();
     }
     Name_pairs::print();
     keep_window_open();
}

However, in int main() when I'm trying to call the functions I get "cannot call 'whatever name is' function without object." I'm guessing this is because it's looking for something like variable.test or variable.read_names. How should I go about fixing this?

Jason Plank · Accepted Answer · 2011-08-24 15:09:08Z

up vote 27 down vote accepted

You need to instantiate an object in order to call its member functions. The member functions need an object to operate on; they can't just be used on their own. The main() function could, for example, look like this:

int main()
{
   Name_pairs np;
   cout << "Enter names and ages. Use 0 to cancel.\n";
   while(np.test())
   {
      np.read_names();
      np.read_ages();
   }
   np.print();
   keep_window_open();
}

edited Aug 24 '11 at 15:09

Jason Plank

2,131 4 25 38

answered Jul 14 '09 at 20:19

sth

146k 36 230 320

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Rob K · Answer 2 · 2009-07-14 20:20:24Z

up vote 14 down vote

If you want to call them like that, you should declare them static.

answered Jul 14 '09 at 20:20

Rob K

7,221 1 22 29

Not possible in this case since all the methods need the object context to access one or more of the member properties names, ages, name, age. (they could be static, too. But then it would be quite useless ;-)) – VolkerK Jul 14 '09 at 20:28

thank you. correct for my case. forgot to put the 'static' keyword – jondinham Aug 23 '12 at 3:53

add a comment

score 1 · Answer 3

You are right - you declared a new use defined type (Name_pairs) and you need variable of that type to use it.

The code should go like this:

Name_pairs np;

np.read_names()

cannot call member function without object

3 Answers

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