C++ Optimal way of returning multidimensional array from function, pointers?

Question

I need to return an array of class objects from a function. I understand from research that the best way to do this is with a pointer, but is this the best way given my program design, and the need to access this from multiple CPP files?

main.cpp

#include <class.h>
#include <functions.h>

int main(){
Class Object[2][]; //define second dimension here?
some_function(); //should return / create the array with filled in elements.
int var = arr[2][3]; // want to be able to do something like this in main
}

functions.cpp

void some_function(){
// assign values
arr[2][3] = 1;
}

Try a vector. vector<vector<int>> some_function() {...} Of course you'll need C++11 to use <int>> and not <int> >. — Qaz
– Qaz, Commented Apr 16, 2012 at 22:16

Tony The Lion · Accepted Answer · 2012-04-16 22:16:17Z

8

You should really use std::vector<std::vector<Object> > for your multi-dimensional array. Using raw arrays is error prone, and since you're using C++ anyways, why not make use of something as useful as the std::vector which automatically resizes when needed.

You can even return the vector from your function like so:

std::vector<std::vector<Object> > my_function() { /* do something */ return some_vector; }

answered Apr 16, 2012 at 22:16

Tony The Lion

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4 Comments

Skrymsli Over a year ago

And if you are using C++11 and Object is moveable this is also optimal (in that you don't copy everything in the vectors). If you aren't using C++11 maybe put your objects into boost or tr1 shared_ptr.

Martin James Over a year ago

Does returning a vector like this, with no pointer, enable the vector array to be returned without any bulk data copying?

R. Martinho Fernandes Over a year ago

@MartinJames given a decent compiler, yes.

suszterpatt Over a year ago

@Martin: yes, look up Return Value Optimization.

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