How to create function with input is 2D array in C++

Question

I have a 2D array that defined as

int P[5][10];
for (int i=0;i<N;i++)
{
    for(int j=0;j<L;j++)
    {
        if(random()>0.5)
            P[i][j]=1;
        else
            P[i][j]=0;
    }
}

I want to make a function with input is P. The function allows us show the value of P. How to defined that function. I tried such as

void show_P(int P[][], int numcols,int numrows)

However, it is wrong. Could you help me fix it? Thanks

Don't use 2D arrays. Use 1D arrays, perhaps encapsulating them in some class which has member functions to access or modify them. — Basile Starynkevitch
– Basile Starynkevitch, Commented Mar 31, 2015 at 5:56
Declare a 1D array or vector, and use a[i*width+j] instead of a[i][j] — Basile Starynkevitch
– Basile Starynkevitch, Commented Mar 31, 2015 at 5:58
You should avoid 2D arrays. It is very likely that you'll get confused. And there is no need for them. — Basile Starynkevitch
– Basile Starynkevitch, Commented Mar 31, 2015 at 6:01
You could always search the net for a proper answer. One I could easily found is here, on stackoverflow: stackoverflow.com/a/8767247/1432385 — Lucaci Andrei
– Lucaci Andrei, Commented Mar 31, 2015 at 6:02

Paul R · Accepted Answer · 2015-03-31 14:19:37Z

3

If you want to restrict the arguments to 5 by 10 2D arrays, you can pass by reference like this:

void show_P(int (&P)[5][10])

This will fail for any other type of array. If you want the function to work for other sizes, you can make it a template.

template <size_t N, size_t M>
void show_P(int (&P)[N][M])

edited Mar 31, 2015 at 14:19

Paul R

214k38 gold badges402 silver badges579 bronze badges

answered Mar 31, 2015 at 5:57

juanchopanza

228k35 gold badges421 silver badges493 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Jame Over a year ago

Is it safety way? That means we don't worry about memory problem. Someone suggest to me using 2D points array. However, I think your suggestion is very simple. Thanks

juanchopanza Over a year ago

@user8430 This has type safety, as mentioned in the answer. A pointer to pointer doesn't have that.

Jame Over a year ago

Good knowledge. Thank you.

Jame Over a year ago

Can your way apply for returning 2D array? That means if I want to write a function to return 2D array, can I apply template <size_t N, size_t M> void set_P(int (&P)[N][M])

juanchopanza Over a year ago

@user8430 There isn't a way to do that, because arrays are not copyable.

|

WindMemory · Accepted Answer · 2015-03-31 05:52:41Z

1

You could just change it to:

void show_P(int** P, int numcols, int numrows)

Passing 2D array always using the pointer.

Hope this will help.

answered Mar 31, 2015 at 5:52

WindMemory

5901 gold badge5 silver badges19 bronze badges

1 Comment

Paul R Over a year ago

This does not solve the OP's problem - you can't pass a 2D array of int as an int **.

4386427 · Accepted Answer · 2015-03-31 06:17:33Z

1

Or using the std::array

void printArray(array<array<int,2>,3>& arr)
{
  for (auto x : arr)
  {
    for (auto y : x)
    {
      cout << y << endl;
    }
  }
}

int main()
{
  array<array<int,2>,3> arr{{{1, 2}, {2, 3}, {3, 4}}};
  arr[0][1] = 5;
  printArray(arr);
}

would give you:

1

5

2

3

4

answered Mar 31, 2015 at 6:17

4386427

44.7k4 gold badges44 silver badges69 bronze badges

Comments

Cpp Programmer · Accepted Answer · 2015-03-31 06:31:35Z

0

void print( int (&ref)[5][10]) {

for( auto &lm: ref) // get the first array from the multidimensional array and initialize lm with it 
    for( auto &elem: lm) // get the first element from lm 
        std::cout << elem << " "; // print the element 

}

This only works with an array with dimensions as P i.e, [5][10]

edited Mar 31, 2015 at 6:31

answered Mar 31, 2015 at 6:14

Cpp Programmer

1268 bronze badges

1 Comment

Cpp Programmer Over a year ago

I have made 'lm' a reference because if we don't then lm will not be a reference to an array but rather have a type of int * which is not that we want it to be.

John · Accepted Answer · 2015-03-31 06:15:39Z

-1

N=5;
L=10;    
void show_P( int ( &P )[N][L] )

edited Mar 31, 2015 at 6:15

answered Mar 31, 2015 at 5:55

John

3,1209 gold badges41 silver badges67 bronze badges

Collectives™ on Stack Overflow

How to create function with input is 2D array in C++

5 Answers 5

7 Comments

1 Comment

Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

7 Comments

1 Comment

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related