2D array bounds checking using std::vector and .at()

Question

I've a quite simple question but for witch I cannot find the answer.

How can I use the .at(i) in a 2D array of vector < vector <type> > ?

I want to have bounds checking - witch .at(i) function provides automatically, but I can only access my array using the array[i][j] witch doesn't provide for bounds checking.

It's a vector of vectors. Just substitute [...] by .at(...). How else should it work? — Christian Rau
– Christian Rau, Commented Oct 10, 2011 at 15:43

NPE · Accepted Answer · 2011-10-10 15:17:42Z

4

The correct syntax to use is:

array.at(i).at(j)

answered Oct 10, 2011 at 15:17

NPE

503k114 gold badges970 silver badges1k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

jbssm Over a year ago

You are right. I had tried that for starters but made other mistake and didn't complite, so I tought that was the problem.

Fred Foo · Accepted Answer · 2011-10-10 15:18:27Z

3

Since .at(i) will return a reference to the vector at v[i], use .at(i).at(j).

answered Oct 10, 2011 at 15:18

Fred Foo

365k80 gold badges765 silver badges852 bronze badges

2 Comments

jbssm Over a year ago

You are right. I had tried that for starters but made other mistake and didn't compile, so I tough that was the problem. Thanks.

Kerrek SB Over a year ago

Reading compiler errors is in equal parts skill and art ... good luck :-)

Sarfaraz Nawaz · Accepted Answer · 2011-10-10 15:41:32Z

2

Use vec.at(i).at(j) and must use this in try-catch block since at() will throw std::out_of_range exception if the index is invalid:

try
{
      T & item = vec.at(i).at(j);
}
catch(const std::out_of_range & e)
{
     std::cout << "either index i or j is out of range" << std::endl;
}

EDIT:

As you said in the comment:

I actually want the program to stop in case the exception is raised. – jbssm 5 mins ago

In that case, you can rethrow in the catch block after printing the message that it went out of range, so that you can know the reason why it stopped. And here is how you rethrow:

catch(const std::out_of_range & e)
{
     std::cout << "either index i or j is out of range" << std::endl;
     throw; //it rethrows the excetion
}

edited Oct 10, 2011 at 15:41

answered Oct 10, 2011 at 15:22

Sarfaraz Nawaz

363k121 gold badges682 silver badges867 bronze badges

3 Comments

jbssm Over a year ago

Thank you. I actually want the program to stop in case the exception is raised.

Sarfaraz Nawaz Over a year ago

In that case, you can rethrow in the catch block after printing the message that it went out of range, so that you can know the reason why it stopped.

Paul Price Over a year ago

In that case, don't try/catch at all.

Collectives™ on Stack Overflow

2D array bounds checking using std::vector and .at()

3 Answers 3

1 Comment

2 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

2 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related