C Arrays – Declaring and Initializing Arrays in C

arraysc++initialization

Is there a way to declare first and then initialize an array in C?

So far I have been initializing an array like this:

int myArray[SIZE] = {1,2,3,4....};

But I need to do something like this

int myArray[SIZE];

myArray = {1,2,3,4....};

In C99 you can do it using a compound literal in combination with memcpy

memcpy(myarray, (int[]) { 1, 2, 3, 4 }, sizeof myarray);

(assuming that the size of the source and the size of the target is the same).

In C89/90 you can emulate that by declaring an additional "source" array

const int SOURCE[SIZE] = { 1, 2, 3, 4 }; /* maybe `static`? */
int myArray[SIZE];
...
memcpy(myarray, SOURCE, sizeof myarray);

Initialize all members to the same value:

int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };

Elements with missing values will be initialized to 0:

int myArray[10] = { 1, 2 }; //initialize to 1,2,0,0,0...

So this will initialize all elements to 0:

int myArray[10] = { 0 }; //all elements 0

In C++, an empty initialization list will also initialize every element to 0:

int myArray[10] = {}; //all elements 0 in C++

Objects with static storage duration will initialize to 0 if no initializer is specified:

static int myArray[10]; //all elements 0

If your compiler is GCC you can use following syntax:

int array[1024] = {[0 ... 1023] = 5};
int A[10] = {[0 ... 4] = 5, [5 ... 9] = 3};