问题
I am still learning C++ and trying to understand it. I was looking through some code and saw:
point3(float X, float Y, float Z) :
x(X), y(Y), z(Z) // <----- what is this used for
{
}
What is the meaning of the "x(X), y(Y), z(Z)" sitting beside the constructor's parameters?
回答1:
It's a way of invoking the constructors of members of the point3 class. if x,y, and z are floats, then this is just a more efficient way of writing this
point3( float X, float Y, float Z):
{
x = X;
y = Y;
z = Z;
}
But if x, y & z are classes, then this is the only way to pass parameters into their constructors
回答2:
In your example point3 is the constructor of the class with the same name (point3), and the stuff to the right of the colon : before the opening bracket { is the initialization list, which in turn constructs (i.e. initializes) point3's member variables (and can also be used to pass arguments to constructors in the base class[es], if any.)
回答3:
Member initialization as others have pointed out. But it is more important to know the following:
When the arguments are of the type float or other built-in types, there's no clear advantages except that using member initialization rather than assignment (in the body of the constructor) is more idiomatic in C++.
The clear advantage is if the arguments are of user-defined classes, this member initialization would result in calls to copy constructors as opposed to default constructors if done using assignments (in the constructor's body).
来源：https://stackoverflow.com/questions/2349978/variables-after-the-colon-in-a-constructor