a question regarding typedef

erikash · 11-10-2005, 03:21 AM

hi, i came across this code:

Code:

#include <stdio.h>

#define N 3
typedef int matrix[N+2][N+2];

void initial_matrix(matrix m) // initiate the matrix
{
	int i,j;
	for (i=0;i<=N+1;i++) 
	{
		for(j=0;j<=N+1;j++) 
		{
		m[i][j] = -1;  //*(&m[0][0]+i*(N+1)+j)
		}
	}
}



void print_matrix(matrix m) // prints the matrix
{
	int i,j;
	for (i=0;i<=N+1;i++) 
		{
			for(j=0;j<=N+1;j++)
				printf("%d ",m[i][j]);
			printf("\n");
		}
}



void main(void) {

matrix mat;
initial_matrix(mat);
print_matrix(mat);
system("pause");

}

guys, could you explain me how exacly the function "initial_matrix(mat)" works? (this code is written in C), why is it affecting the original variable mat?
(and isn't making a copy), what is sent to the function, and how does it receives it?

thanks in advance,
erik

nx5000 · 11-10-2005, 04:37 AM

In C, an array defininition is equivalent to the adress of its first element.
So when you pass an array in parameter, you pass the adress of the first element.

void initial_matrix(int *Matrix)
is the same as your function, you just loose the information of the length.

So you manipulate directly the real matrix, not a copy