Re: pointers and dynamic arrays

Gianni Mariani <>
Sat, 21 Apr 2007 16:56:13 +1000
<4629b58d$0$25473$> wrote:

I'm having some trouble with poitners and dynamic arrays (a matrix).

Given this function I have a few questions.

void func(int* mat, int rows, int columns, char* out)

My first question is in main, how is a matrix defined that can be sent
to this function?

That would probably be expecting mat as a contiguous array of rows...

i.e. element (i,j) is probably

mat[ i* columns + j ] or mat[ i + j * rows ]

The best way to do this is with a matrix class of which there are plenty
of examples on this NG.

I can do it like:

int** matrix;
matrix = new int*[numRows];
for(int i=0; i< numRows; i++)
    matrix[i] = new int[numColumns];

That's not unusual but probably not what is needed here.

and by sending func(matrix,numRows, numColumns, out). But the only
way I can get it to accept this is by changing the first argument to
accept int** instead of int*. It has to accept int* so I'm not quite
sure how to declare a matrix in main.

My next question is how can I set an element of the matrix to a
location of the char* array?

I can easily use cout<<mat[3][3]; in the func and it'll output that
certain element on to the screen, but I can't get it to go to an
element in the character array.

cin >> mat[3][3]; // maybe ?

I know this would be a lot easier to do this with out pointers and
just using arrays and not poitners to arrays so don't tell me that...


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