Passing a 2d-Array with an unknown row and column size to a function (C++)

Question

I got this function so far :

void sumcol(int a[r][c],int r,int c){
int i,j,sum=0;
//int sizec= sizeof(a)/sizeof(a[0][0]);
//int sizer= sizeof(a)/sizeof(a[0]);

for (i=0;i<r;i++){
    for (j=0;j<c;j++) sum=sum+a[j][i];
    cout<<"Suma pe coloana "<<i<<" este : "<<sum<<endl;
    sum=0;
}
}

I get an error on the first line that r and c were not declared in this scope. Why? Though I read right there : https://www.eskimo.com/~scs/cclass/int/sx9a.html that this is a Correct way of declaring.

Pass a pointer and length of the array to your function. The pointer will point at the beginning of some array and the length will tell you how many cells it has (if you want to iterate or something). — rbaleksandar, Sep 05 '15 at 11:00

score 2 · Accepted Answer · edited May 23 '17 at 11:58

I think your real problem is passing 2d array into function. If you know your array size in compile time I will advice something like:

template <int r, int c>
void sumcol(int (&a)[r][c]){
    int i,j,sum=0;
    //int sizec= sizeof(a)/sizeof(a[0][0]);
    //int sizer= sizeof(a)/sizeof(a[0]);

    for (i=0;i<r;i++){
        for (j=0;j<c;j++) sum=sum+a[j][i];
        std::cout<<"Suma pe coloana "<<i<<" este : "<<sum<< std::endl;
        sum=0;
    }
}

and calling it like forexample :

int main()
{

    int temp[3][5]; // You don't forget to initialize this in your real code
    sumcol(temp); 
}

Or if you are using dynamiccally allocated matrix array(malloc). Than use something like:

void sumcol(int** a,int r,int c){
      do stuff

Consider reading this thread first Passing a 2D array to a C++ function

I personally find it easier to do this stuff with cool C++ Vectors instead C arrays .

You don't need to specify the template parameters. You can say `sumcol(temp);` — juanchopanza, Sep 05 '15 at 10:50

Passing a 2d-Array with an unknown row and column size to a function (C++)

1 Answers1