Pass function with 2D array input to a function

Question

I want to pass a function to a function, in which case the passing function has 2D arrays for input.

For 1D arrays I have done like that:

void bungee(double Y[], double DY[])
{
   // ...
}

void euler(void(ODES)(double[], double[]), double A[], double STEP)
{
   // ...

   ODES(A, B);
}

int main()
{
    // ...

    euler(bungee, y, dt);

    return 0;
}

Now I would like to pass bungee to euler with 2D arrays input, like this:

void bungee(double Y[][], double DY[][])
{ // ... }

void euler(void(ODES)(double[][], double[][])/*,...*/)
{ // ... }

int main()
{ 
    euler(bungee);
    return 0;
}

What happens when you do that ? What error do you get ?

Olotiar
– Olotiar

2014-01-11 09:32:04 +00:00
Commented Jan 11, 2014 at 9:32 — Olotiar
– Olotiar, Commented Jan 11, 2014 at 9:32

user534498 · Accepted Answer · 2014-01-11 09:43:36Z

1

in C/C++, arrays will be converted to pointer when passing to function. double Y[] will be same as double *Y.

For two dimentional arrays, you must provide the inner dimension when passing to function.

Because if you pass double Y[][], it will be converted to double (*Y)[], which is an incomplete type.

Instead, double Y[][50], will be converted to double (*Y)[50], which is fine.

For N dimentional array, you must provide the inner N-1 dimensions.

For example, double Y[][10][20][30].

answered Jan 11, 2014 at 9:43

user534498

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1 Comment

Vito Over a year ago

Thanks, that was easy. :D So I did:

const int DIM 50; void bungee(double Y[][DIM], double DY[][DIM]) { //... }  void euler(void(SYS)(double[][DIM], double[][DIM])) { // ... }

mb84 · Accepted Answer · 2014-01-11 10:07:12Z

0

Like user534498 explained for continuous arrays, e.g.

void bungee(double [][50]);

void main()
{
    double array[100][50];
    bungee(array);
}

but if you create your 2D arrays like this

double **arr = new double* [100];
for (int i=0; i<100; i++)
    arr[i] = new double [50];

you must use

void bungee(double **);

answered Jan 11, 2014 at 10:07

mb84

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