Default value for elements of an array of variable size

Question

Is there any way to assign all elements of an array the value 0 in one go.The array accepts its size from the user. Hence

int array[x] = {0};

Won't work!

[`calloc`](http://pubs.opengroup.org/onlinepubs/009695399/functions/calloc.html)? — Jon, Oct 08 '13 at 19:39
@Jon that does a heap allocation. The most direct translation is `alloca`, which is nonstandard but available on most platforms — SheetJS, Oct 08 '13 at 19:41
@Nirk: Stack allocation for something whose size is dictated by the user? I wouldn't. — Jon, Oct 08 '13 at 19:42
[How to initialise array dynamically with a default value?](http://stackoverflow.com/questions/17898703/how-to-initialise-array-dynamically-with-a-default-value/17898722#17898722) — Grijesh Chauhan, Oct 08 '13 at 19:45
if you have circumstances, use vector instead of normal array. — PersianGulf, Oct 08 '13 at 19:48

Mauren · Answer 1 · 2013-10-08T19:50:23.203

0

You will need to dynamically allocate the memory for this array:

int *array;
int x;

scanf("%d\n", &x);

array = malloc(sizeof(int) * x);

then set value for all of them

memset(array, 0, x);

or use calloc:

array = calloc(x, sizeof(int));

edited Oct 08 '13 at 19:50

answered Oct 08 '13 at 19:41

Mauren

1,955
2
18
28

1

Like there wasn't calloc. – zubergu Oct 08 '13 at 19:46
But remember to `free()` it after use. – glglgl Oct 08 '13 at 20:06
@glglgl yep, memory leaks are not ok. – Mauren Oct 08 '13 at 20:14

score 0 · Answer 2 · answered Oct 08 '13 at 19:42

0

int *array;
int i;
printf ("Amount of numbers to be entered: ");
scanf ("%d",&i);

array = (int*) calloc (i,sizeof(int));

answered Oct 08 '13 at 19:42

CS Pei

10,869
1
27
46

Steven Eckhoff · Answer 3 · 2013-10-08T19:57:01.917

0

Use memset

void * memset ( void * ptr, int value, size_t num );

int *array = (int *) malloc(sizeof(int) * x);

memset(array,0,sizeof(int) * x);

OR Use:

void* calloc (size_t num, size_t size);

int *array = (int *) calloc(x, sizeof(int));

edited Oct 08 '13 at 19:57

answered Oct 08 '13 at 19:48

Steven Eckhoff

992
9
18

zubergu · Answer 4 · 2013-10-08T20:16:23.650

My best bet is to use memset from string.h library.

memset(array,0,x*sizeof(int));

This is not technically initialization, because there is no assignment, it only sets all bytes in given memory to '0' but that's exactly what you want to do here.
Also, consider using malloc for creating your array, because the way you do it now, your array will be created on the stack(which has finite capacity) and will be freed when function that creates it returns(just like regular automatic variable). That means your array is inaccessible from outside of its local scope.

Default value for elements of an array of variable size

4 Answers4