CODEWITHSUNDEEP
cmalloc
user10548749
user10548749

Reputation:

Why do I Need to initialize result of malloc on MacOs?

I have implemented a C calculator to analyses input. I have a struct (like a chained list) but on macOS I have to initialise through the init_null function or variable like value have an initial value. I have just one question: why?

On Linux, there was no issues. 

typedef struct node_t {
    int value;
    char operator;
    struct node_t *left;
    struct node_t *right;
} node_t;

node_t *init_null(node_t *root) {
    root->value = NULL;
    root->operator = NULL;
    root->left = NULL;
    root->right = NULL;
    return root;
}

node_t *build_tree(const char *argv[], int *position) {
    node_t *new = malloc(sizeof(node_t));
    new = init_null(new); /*sinon erreur*/

    if (isdigit(*argv[*position])) {
        new->value = atoi(argv[*position]);
    } else/*Opérateur*/  {
        new->operator = *argv[*position];
        *position = *position + 1;
        new->left = build_tree(argv, position);
        *position = *position + 1;
        new->right = build_tree(argv, position);
    }
    return new;
}

When run, ./main * 2 + 3 4 should print (2 * (3 + 4)).

Upvotes: 2

Views: 434

Answers (1)

John
John

Reputation: 1032

Here is the problem:

There are at least 2 memory allocation methods you can use, malloc and calloc. The difference is that malloc DOES NOT initialise (or set) the successfully allocated memory to anything. There is an indeterminate explicit or implicit effect on the memory block, specific to the compiler at this compilation stance, as @EricPostpischil explained.

Whereas calloc sets the successfully allocated memory block to zero. Note that the arguments are slightly different.

Back to your concern, in Linux malloc just happened to allocate a block of memory that had zero in it, whereas on the macos platform there was something in it.

Use calloc if you thing you need it, otherwise do a memset of 0 to the allocated memory block.

Upvotes: 2

Related Questions