C++ lists and pointers

Question

I am working on homework and wanted to know what this is actually defined as:

list < NAME > * m_ofList

Where name comes from a struct like so:

typedef struct name
{
    int age;
    int height;
} NAME;

I want to know what it is so I know how to insert to it or access it: push_back, insert, etc.

So I understand this now, but I am stuck because of some type of memory access: it produces a segmentation fault and I have been unable to figure this out. Where do I need to initialize my new list? it doesn't work in constructor or in the functions. Just FYI, it is a private list so it can only be used for member functions (i.e. m_ofList). I can produce code if anyone would like to help...

Please tell us that list < NAME > * m_ofList and that struct didn't come from the person teaching you C++? — johnsyweb
– johnsyweb, Commented Jun 3, 2012 at 5:17
it did not come from me, so i don't think i can change it... — guy_without_a_name
– guy_without_a_name, Commented Jun 3, 2012 at 5:18

Benjamin Lindley · Accepted Answer · 2012-06-03 05:51:55Z

8

Assuming using namespace std or using std::list, that's a pointer to a list of objects of the class/struct NAME. To put objects in it, first you need to initialize it:

m_ofList = new list<NAME>;

or:

m_ofList = &(some already initialized list of NAME objects);

Then you can put items in it:

NAME x;
x.age = 15;
x.height = 150;
m_ofList->push_back(x);
m_ofList->insert(m_ofList->begin(), x);

If you went with dynamically allocating the list with new, it needs to be properly disposed of when you are done with it:

delete m_ofList;

My question for you is, why is it a pointer in the first place? You could just declare it (as you should) like this:

list<Name> m_ofList;

Then you wouldn't have to worry about disposing of it. It would be taken care of by scoping rules.

edited Jun 3, 2012 at 5:51

answered Jun 3, 2012 at 5:18

Benjamin Lindley

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8 Comments

guy_without_a_name Over a year ago

that helps, however, i get a EXC_BAD_ACCESS when i initialize it (using Xcode) or a seg fault 11 with unix...could you explain that?

Benjamin Lindley Over a year ago

@BrianKnowlton: I would need to see a more complete example. Preferably, completely complete.

UltraInstinct Over a year ago

You get segfaults when you try to access invalid memory locations. Can you use a debugger and show us your backtrace?

guy_without_a_name Over a year ago

Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: 13 at address: 0x0000000000000000 0x0000000100001f5b in CGraph::AddEdge ()

Benjamin Lindley Over a year ago

@BrianKnowlton: When I said "complete example", I was referring to your code, not the error message, sorry for the confusion.

|

Trevor Hickey · Accepted Answer · 2012-06-03 05:40:43Z

Regardless of the data type you chose to hold in your list, the member functions will remain the same.
Documentation regarding what member functions you can call for the STL list container can be found here.
You can create lists that hold any data type because they are built with a construct known as templates. Templates are what allow you to create lists of different data types.
Example:

#include <list>
#include <string>
#include <cstdlib>


int main(){

    //here is a list that can only hold integers
    std::list<int> list1{1,2,3,4,5};

    //here is a list that can only hold characters
    std::list<char> list2{'a','b','c','d','e'};

    //we can create a new type to represent a person
    struct person{
        std::string name;
        int age;
        int height;

        person(std::string const& name_, int const& age_, int const& height_):
        name(name_), age(age_) ,height(height_){}
    };

    //and now that we have a new person type, we can create a list to hold people
    std::list<person> list3{{"John",21,70},{"Jane",20,68}};

    return EXIT_SUCCESS;
}

compiled with g++ -std=c++0x -o main main.cpp

user1431841 · Accepted Answer · 2012-06-03 05:11:44Z

0

In C++, that is most likely an STL List. You can find some documentation here: http://www.sgi.com/tech/stl/List.html

answered Jun 3, 2012 at 5:11

user1431841

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Comments

Eight · Accepted Answer · 2012-06-03 05:20:13Z

0

It is an STL list which is a Linked list of variables, struct or objects. It supports Insert, remove operation at any position.In list < NAME > * m_ofList m_oflist is a pointer to an list of Name objects. here is a good tutorial on STL list.

answered Jun 3, 2012 at 5:20

Eight

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