Teronary operator

[adam2016]

here is the snippet of code I am referring to which is in the copy constructor,I don't understand what the terenry operator is doing hereit is saying if mSize is equal to new int[mSize] let mSize = new int[mSize] else set it to a nullptr,so how does this even work?

 dumb_array(const dumb_array& other)
        : mSize(other.mSize),
          mArray(mSize ? new int[mSize] : nullptr),
    {
        // note that this is non-throwing, because of the data
        // types being used; more attention to detail with regards
        // to exceptions must be given in a more general case, however
        std::copy(other.mArray, other.mArray + mSize, mArray);
    }

[tpb]

No. It says:

if mSize is not equal to 0 then return new int[mSize] else return nullptr

However, it doesn't actually return the value but instead the selected branch becomes the value of the TERNARY expression.

[jlb]

I don't understand what the terenry operator is doing hereit is saying if mSize is equal to new int[mSize] let mSize = new int[mSize] else set it to a nullptr,so how does this even work?

It is not checking mSize to new int[mSize] it is checking whether or not mSize has a value. If it does it creates an array of size mSize, otherwise assigns nullptr to the pointer mArray, this is assuming that mSize is some kind of unsigned type.

[keskiverto]

whether or not mSize has a value

Assuming that mSize is integer type, then it always has some value. (There is no NaN integer.)

The mSize is used as condition expression.

( mSize )
// is essentially
( static_cast<bool>(mSize) )

For integer types that conversion is like:

bool foo( T mSize ) {
  if ( 0 == mSize )
    return false;
  else
    return true;
}

Therefore,

( mSize )
// is like
( 0 != mSize )

IF mSize is not 0
THEN dynamically allocate block of memory (for mSize ints) and initialize dumb_array::mArray with the address of the block
ELSE initialize dumb_array::mArray with nullptr

[adam2016]

thanks guys that makes sense! :)