std::vector<bool> a (b, false); in c#

Question

Can someone please help me understand what the following code means and how it translates to C#?

unsigned int b = 100;
std::vector<bool> a (b, false);

if it was something like this:

vector<bool> a;

I'd probably just go:

List<bool> a;

Is that correct?

But I don't don't know c++, so I don't understand how a uint and a bool are being passed to a vector of type bool? Maybe it should be something like this?

MyGenericList<int, bool> a = new MyGenericList<int, bool>(b, false);

Answer 1

std::vector<bool> is special, it is implemented as a bit array in C++. In other words, 1 byte stores 8 elements of the vector, the most condense possible way to create an array of bool. That's available in .NET as well, the exact equivalent declaration is:

    int b = 100;
    System.Collections.BitArray a = new System.Collections.BitArray(b);

If this array only ever contains 100 elements then, meh, don't bother. If it is going to contain a million then, yes, do bother.

Answer 2

As the other answers say, the C++ code creates something like an array or list with 100 elements, all false . The equivalent in C# would be:

var a = new bool[100];

Or if you don't need a fixed size:

var a = new List<bool>(100);
// or, if the initial capacity isn't important
var a = new List<bool>();

Since the default bool value is false , you don't need to explicitly specify it anywhere. If you wanted true (or, eg in a list of int s, to default to -1 ), you'd have to loop through it after you created it:

var a = new bool[100];
for (var i = 0; i < a.Length; i++)
    a[i] = true;

Answer 3

std::vector<bool> a (b, false); creates a vector (an array or kind of a C# list) that is 100 bools long and initializes these bool s to false.

A note: Do not use std::vector<bool> .

Answer 4

The first argument is the size of vector while second is it's element (see handly C++ reference ). So

std::vector<bool> a(100, false);

Create vector of 100 elements, elements of which are false .

As pointed out by Scarlet std::vector<bool> is 'strange' (it does not have full C++ container interface. I'd not go so far to say 'don't use it' but it's important to know that it might behave strange - the ling above is to 'normal' vector).