problem with push_back

[Fellow]

Hi! I'm not sure about using push_back properly in a program I need to get going:

vector <string> myvector;             // here I'm not sure 

person::person(string n, int a)
{
	name=n;
	age=a;

	set_person(n);
}

int person::get_age()
{
	return age;
}

string person::get_name() const
{
	return name;
}

int person::update_age()
{
	return age+1;
}

person* person::set_person(string n)
{
	myvector.push_back(n);            //it compiles that way
                                          //but I think I don't get what I'm supposed to
	                                  //
                                          //from my previous example; without line 13!
                                          //people.push_back(n);      
}

header:

#ifndef PERSON_H
#define PERSON_H

using namespace std;
class person
{
public:
	vector<person*> people;
	person(string,int);
	person* set_person(string);
	string name;
	int age;
	int get_age();
	int update_age();
	string get_name()const;

};
#endif

main:

#include <cstdlib>
#include <iostream>
#include <string.h>	
///////////////////////////////////////////

#include <iomanip>
#include <vector>
#include "person.h"

using namespace std;

int main()
{
	vector<person*> people;

	bool more=true;
	while(more)
	{
	cout<<"Enter name, q to quit: ";
        
	string name;
	getline(cin,name);
        
        int age;
        
	if(name=="q")
	{
		more=false;
	}
        
	else
	{
		people.push_back(new person(name, age));

	}
	}
        

	for(int i=0; i<people.size(); i++)
	{
		cout<<(*people[i]).get_name();
	}
        
        
        while(!people.empty())
        {
        delete people.back();
        people.pop_back();
        }
system("pause");
return 0;
}

In the version I used people.push_back(n); I got following failure message:

person.cpp:40: error: no matching function for call to 'std::vector<person*, std::allocator<person*> >::push_back(std::string&)'
/usr/include/c++/4.0.0/bits/stl_vector.h:602: note: candidates are: void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = person*, _Alloc = std::allocator<person*>]

kind regards,
Fellow

[Paul McKenzie]

Hi! I'm not sure about using push_back properly in a program I need to get going:

It isn't just push_back() that has issues.

person* person::set_person(string n)
{
	myvector.push_back(n);            //it compiles that way
                                          //but I think I don't get what I'm supposed to
	                                  //
                                          //from my previous example; without line 13!
                                          //people.push_back(n);      
}

Why does this function say it returns a pointer to a person? I see no return value at all.

#ifndef PERSON_H
#define PERSON_H

using namespace std;

A header should not have "using namespace std". The reasons have been discussed here many times, the main one being that if I were to include your header in my C++ module, my module is forced to use the entire std namespace.

Instead, prepend all of the items that are in the std namespace with std::

#ifndef PERSON_H
#define PERSON_H

#include <vector>

class person
{
public:
	std::vector<person*> people;
//...
};

int person::update_age()
{
	return age+1;
}

This doesn't update age. All it does is returns the current age + 1. The current age is not updated.

person.cpp:40: error: no matching function for call to 'std::vector<person*, std::allocator<person*> >:ush_back(std::string&)'
/usr/include/c++/4.0.0/bits/stl_vector.h:602: note: candidates are: void std::vector<_Tp, _Alloc>:ush_back(const _Tp&) [with _Tp = person*, _Alloc = std::allocator<person*>]

Why are you trying to add a string to a vector that takes a person pointer?

Regards,

Paul McKenzie

[Fellow]

I tried:

string person::set_person(string n)
{
	people.push_back(n);            //it compiles that way
                                          //but I think I don't get what I'm supposed to
	return n;                     //
                                          //from my previous example; without line 13!
                                          //people.push_back(n);      
}

and also:

void person::set_person(string n)
{..

but I don't find the fault

I think I'm on the wrong track.
How do I tackle this problem in a skilful way?

[Lindley]

Your error there has nothing to do with the return type of the function, that's a separate issue.

You can't push a std::string into a vector of person*.

[Yadrif]

Usually setter functions take a const reference and return void.

For example:

void person::set_person(const string& n)
{
...
}

I'm not sure if the intention of set_person is to set the person objects name or do something with the storing person objects in the vector.

You have two of vector of person pointers

vector<person*> people;

one in main and one in your person class declaration and a vector of strings.

Hope this helps.

[GCDEF]

I'd wonder why the person class has a vector of type person called people.

What is myVector supposed to accomplish?

I think you need to step back and think about what you're trying to do.

[Lindley]

I'd wonder why the person class has a vector of type person called people.

Perhaps the person is pregnant. With twins.

[Fellow]

yes, that would be nice

[Fellow]

Now I have the following got going:

HEADER
#include <cstdlib>
#include <iostream>
#include <string.h>

/////////////////////////////
#include <vector>

#ifndef PERSON_H
#define PERSON_H

class person
{
public:
	std::vector<person*> people;
	person(std::string,int);
	void person::set_person(const std::string& n);//person* set_person(std::string);
	std::string name;
	int age;
	int get_age();
	int update_age();
	std::string get_name()const;

};
#endif 

CPP
#include <cstdlib>
#include <iostream>
#include <string.h>


//////////////////////////////////
#include <vector>
#include "person.h"

using namespace std;


person::person(string n, int a)
{
	name=n;
	age=a;

	set_person(n);
}

int person::get_age()
{
	return age;
}

string person::get_name() const
{
	return name;
}

int person::update_age()
{
	return age+1;
}

void person::set_person(const string& n)
{  
	vector<person*> push_back(const string& n);              
}
                   
MAIN
#include <cstdlib>
#include <iostream>
#include <string.h>	
///////////////////////////////////////////

#include <iomanip>
#include <vector>
#include "person.h"

using namespace std;

int main()
{
	vector<person*> people;

	bool more=true;
	while(more)
	{
	cout<<"Enter name, q to quit: ";
        
	string name;
	getline(cin,name);
        
        int age;
        
	if(name=="q")
	{
		more=false;
	}
        
	else
	{
		people.push_back(new person(name, age));

	}
	}
        

	for(int i=0; i<people.size(); i++)
	{
		cout<<(*people[i]).get_name();
	}
        
        
        while(!people.empty())
        {
        delete people.back();
        people.pop_back();
        }
return 0;
}

Well, it works somehow.

But honestly I don't know what I'm gathering from all this vector stuff!

Is there something that could be done different? something more worthy to be called engineering ^^

Thanks for the help, by the way

[Lindley]

	vector<person*> push_back(const string& n);

That's not calling a method, that's declaring a function.

Let's start simple: Why do you have a vector of person* called people within your person class? What is this intended to represent?

[GCDEF]

Why is there a people vector inside your person class?
I don't understand what your set_person function is trying to do.
You never get a value for age when you pass it to the person constructor.

[Fellow]

neither do I.
I took the code from any site and tried to grasp what vector is doing.
It was not explained what they are up to do with the people vector!

I didn't care much of this "std::vector<person*> people;" and hoped it would make sense in the end.

Might appear strange, i know. I've just been searching for sites explaining how to implement a person class using templates or vector.

[GCDEF]

Might appear strange, i know. I've just been searching for sites explaining how to implement a person class using templates or vector.

Why? Person implies a single entity. vectors are used for collections. What are you trying to do?

[Fellow]

I'd like to create with vector many persons:
person1
person2
...

"people" could/should be the iterator, shouldn't it?

In

for(int i=0; i<people.size(); i++)
	{
		cout<<(*people[i]).get_name();
	}

I thought "people" as an iterator is already working!?

[Paul McKenzie]

neither do I.
I took the code from any site and tried to grasp what vector is doing.

http://www.cplusplus.com/reference/stl/vector/

I've just been searching for sites explaining how to implement a person class using templates or vector.

What do you mean by searching for sites to implement a person class??? Are there sites dedicated in implementing a Door class, or a Car class, or an Elephant class, or a Globe class, or a BubbleGum class or ..??? You can have an infinite number of ways to implement anything.

You don't learn C++ by "searching sites" and cherry-picking code. Maybe that's why things are not making sense.

Regards,

Paul McKenzie