How to initialize an array of pointer inside a struct by using struct constructor?

Question

I tried memset like

struct TreeNode {
    bool exist;
    bool word_ending;
    TreeNode* branches[3];
    TreeNode(): exist(true), word_ending(false) {
        memset(branches, NULL, sizeof(branches));
    }
};

but there appears warnings

warning: implicit conversion of NULL constant to 'int' [-Wnull-conversion]
        memset(branches, NULL, sizeof(branches));
        ~~~~~~           ^~~~
                         0
1 warning generated.

Is there some other way to initialize the array of pointer to NULL?

If you change NULL to 0 in the source it will compile fine. But just do what NathanOliver suggested. — Millie Smith
– Millie Smith, Commented Sep 14, 2017 at 17:56

NathanOliver · Accepted Answer · 2017-09-14 17:50:34Z

4

Instead of using memset we can initialize the array in the member initialization list. If we use

TreeNode(): exist{true}, word_ending{false}, braches{} {}

Then braches will be zero initialized. This works because each missing initializer in a initialization list causes the corresponding element to zero initialized.

answered Sep 14, 2017 at 17:50

NathanOliver

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6 Comments

danche Over a year ago

Thanks! But how to initialize branches with nullptr? It is not same as 0.

NathanOliver Over a year ago

@danche 0 is the null pointer. nullptr is just 0 casted to the pointer type.

danche Over a year ago

so we don't need branches{nullptr, nullptr, nullptr}?

NathanOliver Over a year ago

@danche You can but you don't need it. braches{} will do exactly what you want.

NathanOliver Over a year ago

braches{} is essentially braches{0, 0, 0} which is essentially branches{nullptr, nullptr, nullptr}

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