Initializing Primitive Array to One Value

Question

Is there a way to initialize an array of primitives, say a integer array, to 0? Without using a for loop? Looking for concise code that doesn\'t involve a for loop.

Answer 1

double A[10] = { value }; // initialize A to value. I do not remember if value has to be compiled constant or not. will not work with automatic arrays

Answer 2

You can use memset if you want all your values to be zero. Also, if you're only looking to initialize to zero, you can declare your array in such a way that it is placed in the ZI section of memory.

Answer 3

int array[10] = {}; // to 0

std::fill(array, array + 10, x); // to x

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Note if you want a more generic way to get the end:

template <typename T, size_t N>
T* endof(T (&pArray)[N])
{
    return &pArray[0] + N;
}

To get:

std::fill(array, endof(array), x); // to x (no explicit size)

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It should be mentioned std::fill is just a wrapper around the loop you're trying to avoid, and = {}; might be implemented in such terms.

Answer 4

There are ways of concealing what you are doing with different syntax, and this is what the other answers give you - std::fill, memset, ={} etc. In the general case, though (excluding compiler-specific tricks like the ZI one), think about what needs to be done by the compiled code:

• it needs to know where your memory block/array starts;
• it needs to set each element of the block to the value in turn;
• it needs to check repeatedly whether the end of the block has been reached.

In other words, there needs to be a loop in a fairly fundamental way.

Answer 5

Yes, it is possible. The initialization method depends on the context.

If you are declaring a static or local array, use = {} initializer

int a[100] = {};  // all zeros

If you are creating an array with new[], use () initializer

int *a = new int[100](); // all zeros

If you are initializing a non-static member array in the constructor initializer list, use () initializer

class C {
  int a[100];

  C() : a() // all zeros
  {
    ...
  }
};

Answer 6

If the number is zero you could also use memset (though this is more C-style):

int a[100];
memset(a, 0, sizeof(a));