Vector of vectors, how to find size?

[Olysold]

How would I edit this to show the size of the inner vector? (Not sure if that is technically correct. Please correct me if it's not)

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<vector<int>> test {{2,3,4,5}, {7,8,9}};

    for (int x = 0; x < test.size(); ++x)
    {
        cout << "Outer Loop" << endl;

        for (int y = 0; y < test.size(); ++y)
        {
            cout << test[x][y] << endl;
        }
    }

return 0;
}

[Peter87]

To get the size of vector test[x] you do test[x].size().

[Catfish3]

test.size(); // size of the outer vector

// size of the inner vector at position 0

test[0].size(); // or
test.at(0).size(); // or
(*i).size(); // where i is an iterator to test[0] 

Nice to see you use C++11 elements!

[vlad from moscow]

#include <iostream>
#include <vector>

using namespace;

int main()
{
    vector<vector<int>> test {{2,3,4,5}, {7,8,9}};

    for ( const auto &v : test )
    {
        cout << "Inner Loop" << endl;

        for ( int x : v )
        {
            cout << x << ' ';
        }
        std::cout << std::endl;
    }

    return 0;
}

In your code there shall be

for (int y = 0; y < test[x].size(); ++y)

instead of

for (int y = 0; y < test.size(); ++y)

[3qX21hU5]

First when you declare vectors of vectors do it like so vector< vector<int> > // Hint: Notice the space between the >'s

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector< vector<int> > test {{2,3,4,5}, {7,8,9}};

    // Prints the first elements size
    // Which means it prints the size of the vector inside the fist element
    cout << test[0].size();

    return 0;
}

You have to remember that each element of the first vector is a vector itself and has all the functionality of a normal vector. So you just need to tell the program which element you want to access the size of and then use the size command.

EDIT: A better example based on your code

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector< vector<int> > test {{2,3,4,5}, {7,8,9}};

    for (auto i = 0; i != test.size(); ++i)
    {
        cout << "Numbers in Element: " << i << endl;
        for (auto j = 0; j != test[i].size(); ++j)
            cout << test[i][j] << " ";

        cout << endl;
    }

    return 0;
}

DOUBLE EDIT: Gezz I'm always to slow :(

[Peter87]

Zereo wrote:

First when you declare vectors of vectors do it like so vector< vector<int> > // Hint: Notice the space between the >'s

Is this a stylistic suggestion? Because in C++11 it's not an error to not use spaces here.

[vlad from moscow]

@Zereo
First when you declare vectors of vectors do it like so vector< vector<int> > // Hint: Notice the space between the >'s

Why shall it be done as you showed?

[LB]

*it is not an error to exclude the space.

[Olysold]

I'm in the midst of the Brain Trust! Thanks people for all the answers =).

@Catfish3 - I'm learning from a C++11 updated book so yeah I'm up with the times! Unless that's sarcasm, then =(. Thanks for the code example. Yours and vlad's helped me figure out how to set up iterators instead. And Peter87 nudged on that.

@Zereo - Yeah the book warned me about the spacing, but it refers to older compilers. Appreciate the explanation, hits the nail in the coffin.

[3qX21hU5]

Is this a stylistic suggestion? Because in C++11 it's not an error to not use spaces here.

*it is not an error to exclude the space.

Why shall it be done as you showed?

Pre C++11 it is a error though so might as well cover your corners. It is a error because Pre C++11 the compiler mistook the two >>'s to mean the >> operator.

Also I guess it doesn't have to be done as shown but a lot of people don't have C++11 compilers and it would be in error for them.

[LB]

If you use any C++11 code you can assume all your code need not worry about C++03 anymore.

[3qX21hU5]

That is true LB, so I guess the proper way of phrasing what I said should have been "Be warned though that if you are not using C++11 you need to declare it like so" instead of "you should declare it like so". My mistake for miss wording it.

[vlad from moscow]

@Zereo
Pre C++11 it is a error though so might as well cover your corners. It is a error because Pre C++11 the compiler mistook the two >>'s to mean the >> operator

It is not serious because using of '>" is not compatible with the previous standard also in some other cases. So there is no any sense to do what you suggested.

Next time do not give bad advices.

[Catfish3]

@ Olysold: No sarcasm, I'm genuinely excited when I see people write C++11 code.

[3qX21hU5]

Next time do not give bad advices.

Ummm... I already admitted I probably phrased it wrong, but I don't see how telling someone that vector<vector<int>> can be in error for older compilers is giving bad advice.

Also have no idea what you are trying to say by

It is not serious because using of '>" is not compatible with the previous standard also in some other cases. So there is no any sense to do what you suggested.

[Olysold]

#Catfish3 - Awesome. Hopefully that's enough to draw you into my threads in the future when I ask questions.

[vlad from moscow]

@Zereo
Also have no idea what you are trying to say by

It is not serious because using of '>" is not compatible with the previous standard also in some other cases. So there is no any sense to do what you suggested.

I said very clear that there are other incompatibiles of using < and > in specifying template arguments between the previous and the current C++ Standards.

[3qX21hU5]

Oh ok now I understand.

And sorry if I sounded rude I just don't really like to be told that I'm giving bad advice when in fact I did no such thing. Specially in that manner. Anyways just wanted to say sorry.