Is there a better way to initialize an allocated array in C++?

Question

How to write this in another (perhaps shorter) way? Is there a better way to initialize an allocated array in C++?

int main(void) {
   int* a;
   a = new int[10];
   for (int i=0; i < 10; ++i) a[i] = 0;
}

Answer 1

 int *a =new int[10](); // Value initialization

ISO C++ Section 8.5/5

To value-initialize an object of type T means:

— if T is a class type (clause 9) with a user-declared constructor (12.1), then the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor);

— if T is a non-union class type without a user-declared constructor, then every non-static data member and base-class component of T is value-initialized;

— if T is an array type, then each element is value-initialized;

— otherwise, the object is zero-initialized

For differences between the terms zero initialization, value initialization and default initialization, read this

Answer 2

How about 3 ways?

1.    int *a = new int[10]();

2.    std::vector<int> a(10, 0);

3.    int *a = new int[10];
      memset(a, 0, sizeof(int) * 10);

Due to popular demand, a couple more:

4.    int *a = new int[10];
      std::fill(a, a + 10, 0);

5.    std::vector<int> a(10);
      std::fill(a.begin(), a.end(), 0);

Answer 3

std::vector<int> vec(10, 0); 
int *a = &vec.front();

Answer 4

You could use memset

Sets the first num bytes of the block of memory pointed by ptr to the specified value (interpreted as an unsigned char).

Answer 5

int main(void) { int *a; a = new int[10]; for(int i=0;i<10;++i) a[i]=0; }

;-)

Answer 6

int *a = (int*) calloc(10, sizeof(*a));

(and check if is NULL, or rewrite a safe wrapper against calloc).

Answer 7

#include <algorithm>

int main() {
    int *a = new int[10];
    std::fill(a, a + 10, 0);
}

Answer 8

Maybe you could try something like this:

int* initIntArray(int size) {
    int *temp = new int[size];
    for(int i = 0; i < size; i++) {
        temp[i]=0;
    }
    return temp;
}

int main () {
    int* a = initIntArray(10);
    int* b = initIntArray(10);
    int* c = initIntArray(10);

    //do stuff with arrays

    delete [] a;
    delete [] b;
    delete [] c;

    return 0;
}

Answer 9

by the way, what about using calloc()? say

int i*=(int[10])calloc(10*sizeof(int))

well i'm just another C guy.. any comment is welcomed here

Answer 10

I'm a C guy and not too sure what "new" really does, but could this work?

int
main( void ) {
   int i = 10;              // start at the far end of the array
   int *a = new int[10]; 
   while ( i-- ) a[i] = 0;  // while ( i == 9, 8, 7, ... , 0 )
}

Just to show off my new loop-counter favorite: while(condition).