struct X
{
X() { std::cout << "X()\n"; }
X(int) { std::cout << "X(int)\n"; }
};
const int answer = 42;
int main()
{
X(answer);
}
I would have expected this to print either
X(int)
, because X(answer);
could be interpreted as a cast from int
to X
, or X(answer);
could be interpreted as the declaration of a variable. However, it prints X()
, and I have no idea why X(answer);
would call the default constructor.
BONUS POINTS: What would I have to change to get a temporary instead of a variable declaration?
nothing at all, because X(answer); could be interpreted as the declaration of a variable.
Your answer is hidden in here. If you declare a variable, you invoke its default ctor (if non-POD and all that stuff).
On your edit: To get a temporary, you have a few options:
The parentheses are optional. What you said is identical to X answer;
, and it's a declaration statement.
如果要声明X类型的变量,则应该这样做:
X y(answer);
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