问题
I wonder if anyone could explain what the default ctor does after memory allocated, how it initializes the allocated memory?
回答1:
I don't know which languange you asked the question for, but I will try to answer anyway for C++ and Java
In C++, it :
- leaves the built-in types (
int,float, pointers, etc.) to an uninitialized value - calls the default constructor on class members
In Java, I think all class members are initialized to their default value (0 or NULL).
回答2:
Default constructors invoke the default constructors of all non-static data members, except those of built-in types, which remain uninitialised.
[2003: 12.1/5]:
A default constructor for a class X is a constructor of class X that can be called without an argument. If there is no user-declared constructor for class X, a default constructor is implicitly declared.
[2003: 12.1/8]:
Default constructors are called implicitly to create class objects of static or automatic storage duration (3.7.1, 3.7.2) defined without an initializer (8.5).
回答3:
Have a look at this (in C and C++ implementation).
Yes, implementation varies from language to language.
来源：https://stackoverflow.com/questions/6773723/what-does-default-constructor-do-when-its-empty