HELP: Function with array passing

neelaka's Avatar, Join Date: May 2008
Newbie Member
Please help find the error in this code.
It probably obvious but I cant seem to find the mistake.

Its a simple call to a function with an array address, but somehow the subsequent addresses of the array elements get messed up.

Please help, urgently needed for a school project.

Thanks a lot.

________________________________________

Code:
#include <math.h>
#include <stdlib.h>
#include <stdio.h>

//Declarations 
typedef float point3D[3]; // declare a point data type for 3D points
typedef float vector3D[3]; // declare a vector data type for 3D vectors


void getNormal(vector3D *normal, point3D p1, point3D p2, point3D p3)
{
	*normal[0]=-10;
	*normal[1]=-2;
	*normal[2]=2;
	
	printf("The addresses inside the function: %i  %i  %i \n", normal[0], normal[1], normal[2]);
	
	printf("The values inside the function:  %f  %f   %f \n\n", *normal[0], *normal[1], *normal[2]);	
}


void main()

{
		//Let P0 = (1, 0, 2)	 P1 = (2, 3, 0)	P2 = (1, 2, 4)
	point3D
		p0 = {1,0,2},	
		p1 = {2,3,0},
		p2 = {1,2,4};

	vector3D n;

	getNormal(&n, p0, p1, p2);


	printf("The addresses returned : %i  %i  %i \n", &n[0], &n[1], &n[2]);
	
	printf("The values returned :  %f  %f   %f \n\n", n[0], n[1], n[2]);;
}

Last edited by shabbir; 14May2008 at 07:40.. Reason: Code block
jayaraj_ev's Avatar, Join Date: Aug 2007
Go4Expert Member
Hi,
In your code getNormal () U r passing address of an array vector3D[3] .So to fill the values in each row of vector3D[3] you should fill it like this
(*normal)[0]=-10;
(*normal)[1]=-2;
(*normal)[2]=2;

because u are not a passing a two dimensional array right!

Inside the function when normal is of type float[*][3] which means normal can take more rows of float[3].
when u find the address of normal
normal[0] = first address float[0][3]
normal[1] = first addr + size of (vector3D)
normal[2] = first addr + size of (vector3D) + size of (vector3D)
so u r trying to find the addres of norma[0][3],normal[1][3], normal[2][3].

for eg
The addresses inside the function: 2293552 2293564 2293576
The values inside the function: -10.000000 0.000000 4.000000

when you note down the address values they will have a difference of 12.

out side the function u r accessing a single dimensional array vector3D[3]

and trying to find out the adress of norma[0],normal[1], normal[2].

The addresses returned : 2293552 2293556 2293560
The values returned : -10.000000 -2.000000 2.000000


from this eg you can also see that address of normal[2] = 2293560 & normal[1][3] = 2293564.
neelaka's Avatar, Join Date: May 2008
Newbie Member
Thanks a lot for the reply,

I got it to work by specifying like this.
I was making a fundamental mistake of thinking something else when infact the name of the array is a pointer itself.


void getNormal(vector3D normal, point3D p1, point3D p2, point3D p3)
{}

void main()
{

vector3D n;
getNormal(n, p0, p1, p2);
}

Thanks again.

Cheers