C++: struct and new keyword

Question

I'm a beginner to C++, I've got the following piece of code:

struct Airline {
    string Name;
    int diameter;
    int weight;
};

Airline* myPlane = new Airline;

my question is when I call the method new it allocates memory, if I recall correctly. How does the PC know how much memory to allocate,especially given that there is a string type in there?

Thanks

Answer 1

An std::string object is fixed-size; it contains a pointer to an actual buffer of characters along with its length. std::string's definition looks something like

class string
{
    char *buffer;
    size_t nchars;

  public:
    // interface
};

It follows that your Airline objects also have a fixed size.

Now, new does not only allocate; it also initializes your object, including the std::string, which means it probably sets the char pointer to 0 because the string is empty.