(badly) implicit ctor calls — var declaration

Q: When do c++ constructors get invoked? Harder to tell than in java.

MyClass a; // calls noarg, behaves exactly like int/float and other builtin types

a = MyClass(); // calls noarg, assignment, and destructor.
// New object created on stack then duplicated in a’s memory location, field by field. New object is then discarded as a STACK var.
// I believe the parentheses are compulsory after the class name.

MyClass arr[9]; // nine constructor calls. no-arg constructor needed! Note the position of [].

MyClass b(a); // calls copier ….. [2]

C c3 = c1; // calls copier, not assignment. same as [2]. Disabled by “explicit” keyword on the copier ctor

C c2;
c2 = c1; // calls assignment, not copier

////// So far, all the variables are nonref stack vars.

MyClass b(); // parsed as a function prototype, not a constructor call

MyClass * ptr; // confirmed no constructor call. The pointer is uninitialized.

MyClass * ptr = 0; // ptr starts off as uninitialized, then it is initialized to 0 i.e. null. You can see these 2 steps by debugging.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s