C : Increase Dynamic Array by one in a loop

Question

I would like to know why I can't reach to increase my array size by only one in a while loop. Here is my code :

void pb_memory(void){
    printf("ERROR : memory problem !\n");
    system("PAUSE");
    exit(EXIT_FAILURE);
}

int main(int argc, char *argv[])
{
             int length = 0;
            /*allocate memory and check for no error*/
            int *array = calloc(1, sizeof(int)); /*initialize to 0*/
            if(array == NULL)
                     pb_memory();

            /*Check for valid inputs and put into array*/
            while((scanf("%d", &num)) != EOF){
                               array[length]=num;
                               length++;
                               array = realloc(array, length*sizeof(int));
                               if(array == NULL)
                                        pb_memory();
            }
.
.
.
.

}

Why is this not working ? It fails and goes directly into the pb_memory() function .I would like every time length increase by one my array does too...

Thanks for your help.

EDIT : Sorry guys I wanted to keep the code simple and focused on my problem that's why I didn't write all my variables. Anyway I'm learning for next time and thanks @Michael and everyone who participate.

How do you know the initial allocation succeeds? And why `int *(array)` and not `int *array`? — StoryTeller - Unslander Monica, Dec 09 '13 at 13:23
I declared length = 0; in my code forgot to write it back and *(array) or *array is not the problem I think — Dovakin940, Dec 09 '13 at 13:28
Try declaring `num` also (see post above about posting real code) — KevinDTimm, Dec 09 '13 at 13:30
This question appears to be off-topic because we can't solve code that we can't see — KevinDTimm, Dec 09 '13 at 13:30

score 1 · Accepted Answer · answered Dec 09 '13 at 13:28

1

You are trying to access to a bad index array[length]=num;, if the size of array is length, you can't access to length-th element.

You have to move the write after the reallocation :

/*Check for valid inputs and put into array*/
while((scanf("%d", &num)) != EOF){
  length++;
  array = realloc(array, length*sizeof(int));
  if(array == NULL)
    pb_memory();
  array[length-1]=num;
}

answered Dec 09 '13 at 13:28

Michael M.

2,556
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Not necessarily a bad answer, but how did you fathom that from the bad code sample in the OP? – StoryTeller - Unslander Monica Dec 09 '13 at 13:31
That was pretty obvious. `length` should be the length of something (ie the array). – Michael M. Dec 09 '13 at 13:36
@Michael, nothing is obvious. Assumption is the mother of all "features". – StoryTeller - Unslander Monica Dec 09 '13 at 13:56

score -1 · Answer 2 · answered Dec 09 '13 at 13:34

-1

Just some thoughts: 1. include some print statements to see exactly where the code fails 2. run gdb with the output the program. For example, in a CLI, run the command "gdb ./a.out" 3. Where is the variable "num" declared ? It suddenly appears in the while-loop's condition ?

answered Dec 09 '13 at 13:34

Mouhcine

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1
2
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This is a comment, not an answer – KevinDTimm Dec 09 '13 at 13:35
To comment, I need 50pts reputation minimum, which I don't have. So I can't comment ... but I can answer – Mouhcine Dec 09 '13 at 13:36

C : Increase Dynamic Array by one in a loop

2 Answers2