Vector of Arrays in C++

[claire.bell1]

Hi,
Im having lots of problems trying to implement a vector of arrays in C++.
Im trying to make a vector that will hold coordinates. Ive decided to
implement a coordinate as an array of integers of length 2.
My code to initialise this array is:
vector<int[2]> coordVector;
This seems to compile ok but im not sure if it is making a vector of arrays
because the command:
coordVector.pus h_back({0,0}) does not work.

Im sure im just doing something simple wrong but im having a nightmare
trying to fix it. Does anyone have any example code that uses a vector of
arrays that i could look at?

Thanks,
Vipa.

[Mike Wahler]

Re: Vector of Arrays in C++


claire.bell1 <claire.bell1@n tlworld.com> wrote in message
news:clINa.6330 $4O4.434840@new sfep2-win.server.ntli .net...[color=blue]
> Hi,
> Im having lots of problems trying to implement a vector of arrays in C++.[/color]

I'm not surprised. Containers require that the elements they
contain be copyable and assignable. Arrays do not meet this
requirement. You're already using a container (vector), so
why are you using an array? How about a vector of vectors?
[color=blue]
> Im trying to make a vector that will hold coordinates. Ive decided to
> implement a coordinate as an array of integers of length 2.[/color]

IMO a poor decision. Either create a 'coordinate' type (class),
or if you only need 'raw' storage for two values, use a 'std::pair'
[color=blue]
> My code to initialise this array is:
> vector<int[2]> coordVector;
> This seems to compile ok but im not sure if it is making a vector of[/color]
arrays[color=blue]
> because the command:
> coordVector.pus h_back({0,0}) does not work.[/color]

(If it were allowed) the element type is 'int[2]', so
'push_back()'s argument must be this type or a type
convertible to it. {0, 0} is not a valid expression
except as an array initializer. It certainly does
not have type 'int[2]'.
[color=blue]
>
> Im sure im just doing something simple wrong[/color]

Yes, you're trying to store noncopyable, nonassignable
items in a container.
[color=blue]
>but im having a nightmare
> trying to fix it.[/color]

As long as you continue to try to break the language
rules, the nightmares will continue.
[color=blue]
> Does anyone have any example code that uses a vector of
> arrays that i could look at?[/color]

Nope, because that's illegal.

Try:

#include <iostream>
#include <ostream>
#include <utility>
#include <vector>

typedef std::pair<int, int> coord_t;
typedef std::vector<coo rd_t> coord_list_t;

std::ostream& operator<<(std: :ostream& os,
const coord_t& coord)
{
return os << coord.first << ", " << coord.second;
}

std::ostream& operator<<(std: :ostream& os,
const coord_list_t& lst)
{
for(coord_list_ t::size_type i = 0; i != lst.size(); ++i)
os << lst[i] << '\n';

return os;
}

int main()
{
coord_list_t coordVector;
coordVector.pus h_back(coord_t( 0, 0));
coordVector.pus h_back(coord_t( 42, 25));
coordVector.pus h_back(coord_t( 18, 69));

std::cout << coordVector << '\n';
return 0;
}


BTW which C++ book(s) are you reading? Perhaps you
need better ones.

-Mike