which is best way to initialize array, “memset” or “ {//value} ”?

Question

int main(){

int ar[50]={1};

//OR

int br[50];

memset(br, 1, sizeof(br)); 

return 0;

}

Answer 1

suppose you do

int ar[50] = {-1};

Now you will expect this line to initialize all array elements with -1 but it will not. It will only set the first element of array to -1 and rest to 0. Whereas memset will show the expected behaviour.

See this Initialization of all elements of an array to one default value in C++? for more info.

let's take an example:-

int arr[5] = { 1, 2 }; // this will initialize to 1,2,0,0,0



int ar[5] = {  }; // this will  initialize  all elements 0



int myArray[10] = {}; // his will also all elements 0 in C++ not in c

So If you want to initialize a specific value to an array use memset().

If you want to initialize all elements in an array to 0 use

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

Because objects with static storage duration will initialize to 0 if no initializer is specified and it is more portable than memset().

Also, The int ar[50]={0}; will be infinite because it just initializes the array and does not have an ending but in memset(arr,0,sizeof(br)) it has the correct way of ending the loop in arrays

Answer 2

int ar[50]={1};

This will set only the first element to 1 . Rest all will be 0 .

memset(br, 1, sizeof(br));

This will set all the bytes in br to 1. It is not the same as setting all the values to 1 . The values afterwards are:

{16843009, 16843009, 16843009, 16843009, 16843009}

Use memset when you know you really need it. It is not exactly made for initializing arrays, it just set the memory to a particular value.

Best way in C++? Use std::fill or std::fill_n .

Example:

int array[5];
std::fill(array, array + 5, 8);

Array now contains:

{8, 8, 8, 8, 8}

Using fill_n

std::fill_n(array, 5, 99);

Array now contains:

{99, 99, 99, 99, 99}

As a side note, prefer using std::array instead of c-style arrays.

Try on godbolt: https://godbolt.org/z/DmgTGE

References:
[1]: Array Initialization
[2]: memset doc