c language printing out value in pointer? [duplicate]

Question

I am trying to print out values in integer pointer. This pointer stores binary search tree keys inorder way.

So my inorder function is,

int traversal(int* num,node *t, int i) {

    if (t == NULL) {
        return i;
    }
    if (t->left != NULL) {
        i = traversal(num, t->left, i);
    }
    num[i] = &(t->value);
    i++;
    if (t->right != NULL) {
        i = traversal(num, t->right, i);
    }
    return i;
}

And print function is,

void traversalPrint(int* nums) {
    for (int i = 0; nums[i] !='\0'; i++) {
        printf("%d", &nums[i]); 
    }

}

int main(){
    int* numPtr = (node*)malloc(sizeof(int*));
    node* bst = NULL:
    traversal(numPtr, bst, 0);
    traversalPrint(numPtr);
}

My issue is traversalPrint function prints out numPtr's memory address, not value. How can I print out pointer's value? Thanks in advance!

The & in &nums[i] gives you back the memory address. It's only needed for strings. — Mateen Ulhaq
– Mateen Ulhaq, Commented Oct 1, 2017 at 19:41
@0decimal0 any reason you don't vote to close as duplicate and just put a comment? — bolov
– bolov, Commented Oct 1, 2017 at 19:41

Stephan Lechner · Accepted Answer · 2017-10-01 19:58:15Z

1

The issue concerning "printing addresses" is that with printf("%d", &nums[i]), you actually take the address of "something". Note that &anObject gives you the memory address of anObject, and &nums[i] gives the memory address of nums[i] (which is the address of the i'th element of nums). BTW: %d is the wrong format specifier for pointer values, and you actually yield undefined behaviour by doing so.

For printing the integral value, use printf("%d", nums[i]) instead.

Note further that the code in your main function does not allocate anything for nums, such that your program will write to non-initialized memory and will again yield undefined behaviour.

use at least int* numPtr = calloc(MAXNODES, sizeof(int)) instead, thereby making sure that every entry is initialized with 0. Otherwise, your comparison in nums[i] !='\0' (which, BTW, should be written as nums[i] != 0) will probably fail, again leading to UB later on.

answered Oct 1, 2017 at 19:58

Stephan Lechner

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1 Comment

jayko03 Over a year ago

I edited numPtr as numPtr = (node*)malloc(sizeof(int)); and tried. but does not have any luck. Then I changed it as you described numPtr=calloc(sizeof(node*), sizeof(int)); but not luck as well. Is MAXNODES same as sizeof(node*) or do you mean something different?

frslm · Accepted Answer · 2017-10-01 19:40:54Z

0

Try nums[i] instead of &nums[i].

answered Oct 1, 2017 at 19:40

frslm

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