using memset to initialise the int array

Question

#include<bits/stdc++.h> 
using namespace std;
int main()
{
    int arr[1010];
    memset(arr,1,sizeof(arr));
    cout<<arr[1]<<endl;
    return 0;
}

I am trying to initialise the array with value of 1. I expect my o/p to be 1. But I got some random number(16843009) as o/p of program.I am not understanding what's wrong with the code???

I am getting the expected answer while I am trying to initialise the array with values -1 and 0. Is it possible to initilise the int array using memset with value other than -1 and 0?????

Use memset only if you want to zero-out memory. As mentioned above - it does only work on bytes, thats why you get that value: `0x01010101 == 16843009`. — Shachar Ohana, Feb 18 '17 at 07:27
Also `using namespace std` is bad See [here](http://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) — Ed Heal, Feb 18 '17 at 07:27
Also, using `#include`is [equally bad](http://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) — Bo Persson, Feb 18 '17 at 10:38
And in C++ you have [`std::fill`](http://en.cppreference.com/w/cpp/algorithm/fill) for filling with values (and not just bytes). — Bo Persson, Feb 18 '17 at 10:40

score 2 · Accepted Answer · answered Feb 18 '17 at 07:27

2

memset sets individual bytes, not entire integers which, typically, span four bytes. If you look at the bits of the number 16843009, it is what you get with four bytes with the value 1. As Ed Heal said, don't complicate things by using memset. Use a loop instead.

answered Feb 18 '17 at 07:27

Thomas Padron-McCarthy

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thanx... but is there any other to initialise instead of using for loops.. the reason i am asking this is .... if i am having 5-d array... i need to write 5 for nested statements in order to initialise the array... can i do it by writing smaller code.. – satyam shekhar Feb 21 '17 at 08:46
@satyamshekhar: You _could_ use a single loop, but that will be code that is both obfuscated and brittle, and perhaps not even guaranteed to work correctly. Don't complicate things. If you have a five-dimensional array, use five nested loops. – Thomas Padron-McCarthy Feb 21 '17 at 13:39

using memset to initialise the int array

1 Answers1