Double pointer to 2D array

[csripriya1]

Hi all,
I have a function which takes 2D -array as an argument. When I try to pass a double pointer as an argument ,VC 6.0 complains that the conversion is not possible.
This is how my function looks like
void slope(int a[][2],float slop[],unsigned long );
I used double pointer to dynamically allocate memory.

int **points=NULL;
points= new int* [nvertices+1];
for(i=1;i<=nvertices;i++)
points=new int [2];

this is the function call
slope(points,slop,nvertices);

Can you please help me with this.

Thanks for your time and help.

 

[Cagliostro]

points=new int* [2];

Ion Filipski

ICQ: 95034075
AIM: IonFilipski
filipski@excite.com

 

[Cagliostro]

sorry, forget first post,
function expets as argument a constant pointer.
you chould change
void slope(int** a,float slop[],unsigned long );

Ion Filipski

ICQ: 95034075
AIM: IonFilipski
filipski@excite.com

 

[ArkM]

It's a very curious part of C/C++ definition: array of array types. Type of a in slope is array of array of int pairs, not int**. We can't declare or directly allocate any objects of this type because sizeof(type) is unknown. But slope prototype gets only int [nnn][2] arrays! We can:
typedef int Ipair[2];
Ipair* points = new Ipair[nvertices+1];
slope(points...
It's OK for C/C++.
Moral(?): hard use multi-dim arrays? Go to FORTRAN or learn STL containers...

 

[palbano]

One point is that the function signature could be described as sloppy from a C++ design standpoint.
void slope(int a[][2],float slop[],unsigned long );

At least define a structure containing the two int values per element and then use a pointer to single array of structures. Or better yet as ArkM states use the STL containers.

struct intpair{
 int a;
 int b;
};

slope( intpair* ptr, float slop[], unsigned long)

Now this still seems sloppy since you don't have any direct size or length information for both arrays. This is a nother reason to use STL containers. Bottom line, don't figure out how to pound a square peg into a round hole. Fix the design.

&quot;But, that's just my opinion... I could be wrong.&quot;

-pete

 

[csripriya1]

Hi all,
Thanks for your suggestions.I corrected my code accoringly.Thanks again.