Initializing multidimensional array C++

Question

In C++, when I want to initialize an array of some length (of integers for instance) I can just write

int* tab;
tab = new int[size];

where size is given somewhere else. But how do I do that in the same manner, when it comes to a multidimensional array? I can't just add another dimension(s) in the second line, because compiler doesn't like that...

It's a simple question I guess. I need that, as I'm writing an assignment in object-oriented programming and 2D array is a private part of a class, which needs to be... constructed in the constructor (with 2 dimensions as parameters).

Please see this: learncpp.com/cpp-tutorial/65-multidimensional-arrays — Lucian
– Lucian, Commented Dec 30, 2014 at 10:21
I've heard about vector, but I wanted to know if there's a way similiar to what can be done with one dimensional array... — Jules
– Jules, Commented Dec 30, 2014 at 10:27
"I've heard about vector". So you've heard about C++, now it's time to really learn it. — n. m. could be an AI
– n. m. could be an AI, Commented Dec 30, 2014 at 10:46

Jarod42 · Accepted Answer · 2014-12-30 10:31:51Z

3

Using std::vector is the safe way:

std::vector<std::vector<int>> mat(size1, std::vector<int>(size2));

if really you want to use new yourself:

int** mat = new int*[size1];
for (std::size_t i = 0; i != size1; ++i) {
    mat[i] = new int[size2];
}

And don't forget to clean resources:

for (std::size_t i = 0; i != size1; ++i) {
    delete [] mat[i];
}
delete[] mat;

answered Dec 30, 2014 at 10:31

Jarod42

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6502 · Accepted Answer · 2014-12-30 10:31:13Z

2

If you can afford std::vector instead of arrays you can use as syntax:

std::vector< std::vector<int> > matrix(rows, std::vector<int>(columns));

for (int i=0; i<rows; i++) {
    for (int j=0; j<columns; j++) {
        matrix[i][j] = i+j;
    }
}

answered Dec 30, 2014 at 10:31

6502

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Comments

paul · Accepted Answer · 2014-12-30 10:36:35Z

0

If you get height/width parameters before the initialization of the array you can try:

int height = 10;
int width = 10;

//...

int tab[heigth][width];

edited Dec 30, 2014 at 10:36

answered Dec 30, 2014 at 10:25

paul

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2 Comments

Öö Tiib Over a year ago

you can not have run-time values as dimensions of automatic array.

Jarod42 Over a year ago

That requires non standard extension: VLA.

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