I need to dynamically create an array of integer. I've found that when using a static array the syntax
int a [5]={0};
initializes correctly the value of all elements to 0.
Is there a way to do something similar when creating a dynamic array like
int* a = new int[size];
without having to loop over all elements of the a array? or maybe assigning the value with a for loop is still the optimal way to go? Thanks
Sure, just use () for value-initialization:
int* ptr = new int[size]();
(taken from this answer to my earlier closely related question)
std::uninitialized_fillI'd do:
int* a = new int[size];
memset(a, 0, size*sizeof(int));
memset? Albeit that memset will no doubt be machine optimised.
memset will generate a warning for non-trivial types. Here, the int is trivial, so it works. For other types, that may have a non-default constructor, or default initialized fields, this will produce a warning, with a suggestion to use value initialization.I'd advise you to use std::vector<int> or std::array<int,5>
Value initialize the elements with ()
Example:
int *p = new int[10]; // block of ten uninitialized ints
int *p2 = new int[10](); // block of ten ints value initialized to 0
To initialize with other values than 0,
for pointer array:
int size = 10;
int initVal = 47;
int *ptrArr = new int[size];
std::fill_n(ptrArr, size, initVal);
std::cout << *(ptrArr + 4) << std::endl;
std::cout << ptrArr[4] << std::endl;
For non pointer array
int size = 10;
int initVal = 47;
int arr[size];
std::fill_n(arr, size, initVal);
Works pretty Much for any DataType!
!Be careful, some compilers might not complain accessing a value out of the range of the array which might return a non-zero value
int *a=new int[n];
memset(a, 0, n*sizeof(int));
That sets the all the bytes of the array to 0. For char * too, you could use memset.
See http://www.cplusplus.com/reference/clibrary/cstring/memset/ for a more formal definition and usage.
std::vector? This would initialise all values to zero (or any other value you choose)