Can I create a 'CopyArray' function that can copy 2d arrays of any size?

Question

In my program I have the need to copy 2d arrays of lengths array[3][8] and array[3][3]. Because of the way I have had to set my parameters I haven't been able to do this in one function so I instead have 2 currently.

void copyArray(float arrayA[][8], float arrayB[][8])
{
    for (int a = 0; a < 3; a++)
    {
        for (int b = 0; b < 8; b++)
        {
            arrayA[a][b] = arrayB[a][b];
        }
    }
}

void copyArray(float arrayA[][3], float arrayB[][3])
{
    for (int a = 0; a < 3; a++)
    {
        for (int b = 0; b < 3; b++)
        {
            arrayA[a][b] = arrayB[a][b];
        }
    }
}

Is there a way to condense this into one function instead of having these 2 very similar functions?

Easier solution: Use std::vector or std::array. If you are stuck using raw arrays, pass the dimensions a and b separately, then you can have a single function for any shaped array. — Cory Kramer
– Cory Kramer, Commented Nov 17, 2014 at 12:55
While I agree with the previous commenter (to use std::vector or std::array), it could be done by making copyArray a templated function (where the template arguments is size_t for the dimensions). — Some programmer dude
– Some programmer dude, Commented Nov 17, 2014 at 12:57

molbdnilo · Accepted Answer · 2014-11-17 13:10:31Z

2

If you pass arrays by reference, you can usefully specify all their dimensions, and if you define a template function, you can use template parameters for those dimensions.

Like this (generalised for the element type as well):

template<typename T, size_t x, size_t y>
void copyArray(T (&arrayA)[x][y], const T (&arrayB)[x][y])
{
    for (int a = 0; a < x; a++)
    {
        for (int b = 0; b < y; b++)
        {
            arrayA[a][b] = arrayB[a][b];
        }
    }
}

This can probably be replaced with a one-liner in C++ 11, but the template would follow the same principle.

answered Nov 17, 2014 at 13:10

molbdnilo

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3 Comments

Some programmer dude Over a year ago

If I may make a suggestion, then you should make arrayB constant.

molbdnilo Over a year ago

@JoachimPileborg Right you are. (I even made the "reverse copy" mistake as I was testing that... The shame. The horror.)

sam Over a year ago

This has worked, however I'm unfamiliar with templates. Could you briefly explain what it is doing here?

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