Adding a object having a string member to a vector

Question

class A
{
public:
    string  name;

    float   length;

    float   weight;

    bool    isEnabled;
};

When I'm doing push_back() on the vector of this class, it works for the first time, but doesn't on the subsequent push_back() calls. Could it be because of the string member? If so, why?

Welcome to SO! Please explain what exactly you mean when you say it doesn't work. Also, if you could show us some more code, that'll probably help to get good answers. — NPE, Jan 03 '12 at 14:20
To clarify, with string do you mean std::string, right? As the others say, it just works. What compiler do you use? — Mr Lister, Jan 03 '12 at 14:24
My bet would be on a `vector`, and associated improper manual memory management. Deleting an `A` whose address is still in such a vector will cause the dtor of `name` to run. — MSalters, Jan 03 '12 at 14:52

score 1 · Answer 1 · answered Jan 03 '12 at 16:12

I tried out your code.

vector<Aclass>  aClass;
aClass.push_back(Aclass("John Doe ", 6.2 , 220  , true) );
aClass.push_back(Aclass("John Doe2 ", 6.2 , 220  , true) );
aClass.push_back(Aclass("John Doe3 ", 6.2 , 220  , true) );
aClass.push_back(Aclass("John Doe4 ", 6.2 , 220  , true) );

But could not replicate your error.

This code pushes back four times.

#include <iostream>
#include <vector>
#include <string>
using namespace std;

class Aclass
{
public:
    string  name;
    double   length;
    double   weight;
    bool    isEnabled;

    Aclass(){}
    ~Aclass(){}

    Aclass(string  _name, double   _length, double   _weight, bool    _isEnabled )  //constructor
    {
        name = _name;
        length = _length;
        weight = _weight;
        isEnabled = _isEnabled;

        cout<<" \n";
        cout<<"Name   : "<<name<<" \n";
        cout<<"length : "<<length<<" \n";
        cout<<"weight : "<<weight<<" \n";
        cout<<" \n";
    }



};



int main()
{ 

    vector<Aclass>  aClass;
    aClass.push_back(Aclass("John Doe ", 6.2 , 220  , true) );
    aClass.push_back(Aclass("John Doe2 ", 6.2 , 220  , true) );
    aClass.push_back(Aclass("John Doe3 ", 6.2 , 220  , true) );
    aClass.push_back(Aclass("John Doe4 ", 6.2 , 220  , true) );

    cout<<" \n";


return 0;
}

Output :

Name   : John Doe
length : 6.2
weight : 220


Name   : John Doe2
length : 6.2
weight : 220


Name   : John Doe3
length : 6.2
weight : 220


Name   : John Doe4
length : 6.2
weight : 220


Press any key to continue

score -3 · Answer 2 · answered Jan 03 '12 at 14:25

-3

Why would the string have anything to do with it ?

Have you done #include <string> ? You haven't mentioned whether your class has a copy constructor. It goes something like this:

class A {
public:
        A() //default constructor
        A(const A&) //copy constructor
};

By default, c++ will copy all public members, but you need to have a copy constructor in order to use STL containers and push_back()

answered Jan 03 '12 at 14:25

viraj

1,784
4
35
52

1

I can only test with MSVC 2005 here, but it works without explicit constructors. – Mr Lister Jan 03 '12 at 14:26
Works for me too, but since the OP gives no mention as to the exact error that he's getting, or the platform/compiler that he's using, this seemed the most likely problem. – viraj Jan 03 '12 at 14:30
@MrLister it's not only MSVC 2005 it also works in [other compilers](http://ideone.com/ERYYO). That's because the default copy constructor is enough for this class. (I'm assuming std::string obviously) – João Portela Jan 03 '12 at 14:45
2

Not an answer but just poor guesswork and advice. They way the OP has declared the class, it should work fine with the compiler generated copy constructor – parapura rajkumar Jan 03 '12 at 14:48

Adding a object having a string member to a vector

2 Answers2