How to initialize a vector of vectors on a struct?

Question

If I have a NxN matrix

vector< vector<int> > A;

How should I initialize it?

I've tried with no success:

 A = new vector(dimension);

neither:

 A = new vector(dimension,vector<int>(dimension));

You should probably consult an introductory book. new returns a pointer to what it has allocated (and is not needed here anyway). — Borgleader, Feb 09 '14 at 18:46
This question is not a duplicate. The supposed linked duplicate is for a different question, for which the top answer also answers this question, but you won't find it when searching for this question. — smrdo_prdo, Aug 19 '16 at 22:07

score 112 · Accepted Answer · edited Jul 28 '16 at 07:41

112

You use new to perform dynamic allocation. It returns a pointer that points to the dynamically allocated object.

You have no reason to use new, since A is an automatic variable. You can simply initialise A using its constructor:

vector<vector<int> > A(dimension, vector<int>(dimension));

edited Jul 28 '16 at 07:41

activatedgeek

answered Feb 09 '14 at 18:47

Joseph Mansfield

Ok, I found my problem. I didn't mention that I have a pointed struct, which have that vector. And doing what u say: myStructVble->A(dimension, vector(dimension)); , it throws me "function doesn't match". – anat0lius Feb 09 '14 at 18:57
3

@LiLou_ You'll have to initialise it the struct's constructor. Or copy from a temporary to the member: `myStructVble->A = vector>(dimension, vector(dimension));` – Joseph Mansfield Feb 09 '14 at 19:00

score 14 · Answer 2 · answered Feb 09 '14 at 18:48

14

Like this:

#include <vector>

// ...

std::vector<std::vector<int>> A(dimension, std::vector<int>(dimension));

(Pre-C++11 you need to leave whitespace between the angled brackets.)

answered Feb 09 '14 at 18:48

Kerrek SB

2 Answers2