C -- Trouble with pointers

Question

I am new to C, know some Java. Trying to write a program that accepts 2D array that represents a directed adjacency matrix, and two numbers, scans the array and returns true if there is a directed path between them (top-down).

I am running into a problem with C implementation. Apparently I have to use pointers to values in array, whilst in Java I could've use values from array (compare, return to function, etc).

I'm pretty sure the logic is in place, I just need help with allocating '*'s in the right places and amounts.

Here's the code:

#include <stdio.h>

#define N 12

typedef int bool;
enum {false, true};

typedef struct adj_mat{
    int A [N][N];
}adj_mat;



int path(struct adj_mat A, int origin, int dest){
    int i;
    if (origin == dest) return true;
    for (i = 0; i < sizeof(A);i++){
        if (A[origin][i]){
            return path (A, i, dest);
        }
    }
    return false;
}

Thanks in advance.

You need sizeof A / sizeof *A to get number of elements of A. — pmg
– pmg, Commented Apr 26, 2015 at 16:39
You should not typedef bool yourself. Use stdbool instead (and use C99 or C11 standard). And why use a typedef for the struct when using struct-domain name lateron? — too honest for this site
– too honest for this site, Commented Apr 26, 2015 at 17:21

timrau · Accepted Answer · 2015-04-26 16:39:31Z

2

for (i = 0; i < sizeof(A);i++){

This should be for (i = 0; i < N; i++){.

Also, your algorithm may not terminate since it didn't take care of cycles in graph.

answered Apr 26, 2015 at 16:39

timrau

23.1k4 gold badges55 silver badges67 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Alexander Over a year ago

Thank you. Feel so stupid, especially since I went out and declared it from the beginning. :)

typ1232 · Accepted Answer · 2015-04-26 16:41:24Z

0

sizeof(A)

This probably does not give you what you expect. It is the number of bytes, not the number of elements.

A[origin][i]

Here you are trying to index the struct adjmat which doesn't work. You probably wanted to index the member A. Try:

A.A[origin][i]

It would probably be a good idea to rename adj_mat A to something else to avoid confusion.

You should also pass the address of A to the function and use adj_mat* as the argument type. If I understand correctly you want the recursion to operate on the same object.

answered Apr 26, 2015 at 16:41

typ1232

5,6136 gold badges40 silver badges56 bronze badges

1 Comment

Alexander Over a year ago

Thank you. I have to use A for an assignment, I dislike it as well.

Collectives™ on Stack Overflow

C -- Trouble with pointers

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related