Array declaration and initialization with structs

Question

I am trying to declare an array of structs, is it possible to initialize all array entries to a default struct value?

For example if my struct is something like

           typedef struct node
           {    int data;
                struct node* next;
           }node;

Is there a way to declare data to 4 and next to null? What about 0 and null?

If you mean "int data = 4;", the answer is NO. Not in C. stackoverflow.com/questions/13716913/… — Vaibhav Desai
– Vaibhav Desai, Commented Oct 6, 2013 at 20:10
Ok so if it isn't possible how would I check if next is empty? Just a simple NULL check or what? — Paul the Pirate
– Paul the Pirate, Commented Oct 6, 2013 at 20:13

Kerrek SB · Accepted Answer · 2013-10-06 20:08:58Z

3

Sure:

node x[4] = { {0, NULL}, {1, NULL}, {2, NULL}, {3, NULL} };

Even this should be fine:

node y[4] = { {0, y + 1}, {1, y + 2}, {2, y + 3}, {3, NULL} };

answered Oct 6, 2013 at 20:08

Kerrek SB

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7 Comments

Paul the Pirate Over a year ago

But what if I have 100,000 entries in my array? Is there a more efficient way?

Bathsheba Over a year ago

For 100,000 entries you'd probably initialising from persistent storage so efficiency would not be a concern as the performance would be io-bound. Kerrek SB's answer stands as 'most likely the best solution' in my opinion so gets +1.

WhozCraig Over a year ago

@Bathsheba +1 I concur. There is no way via some magic declaration to initialize a sequence that increments ad-nausem to some declared upper-bound. Even a regular fixed trivial array, int ar[N] has the same restriction. The structure doesn't add extra complexity to that which is fundamentally impossible to begin with.

Paul the Pirate Over a year ago

So what happens if I have an array of nodes and I check to see if the array indices are null?

Kerrek SB Over a year ago

@PaulthePirate: Re 100000 entries: If you really want to initialize them, then you must spell out the initializer. If you're happy to assign the values after initialization, you can do it in a simple loop. (In C++ you could use templates to produce compact initializers, though.)

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