CODEWITHSUNDEEP
c++classobject
Gaurav
Gaurav

Reputation: 1

class object's declaration confucion

whats is the difference between these three statements in c++ ??
aa *obj;   
aa *obj1 = new aa; 
aa *obj2 = new aa();

where aa is a class I am confucion in last two statement .

Upvotes: 0

Views: 42

Answers (1)

JDługosz
JDługosz

Reputation: 5642

The first does not initialize the pointer.

In the latest specification,

  • If the new-initializer is omitted, the object is default-initialized (8.5); if no initialization is performed, the object has indeterminate value.
  • Otherwise, the new-initializer is interpreted according to the initialization rules of 8.5 for direct initialization.

That is, if the class (you said it was a class) doesn't have a constructor, then the first form will act the same as a local scope definition and leave the memory un-initialized.

The empty initializer will force it to be initialized anyway, which gives the same results as a global variable of that type.

A class might not have a constructor, even a hidden constructor, if it contains nothing but data members of primitive types. You'll see that discussed as a "POD", or plain'ol data. For templates, the difference was found to be annoying, so the rules were refined to work, with (), uniformly for any type, even built-in types. new int() will give a pointer to a value holding 0. new int will give a pointer to a value holding whatever garbage happened to be at that address before.

Upvotes: 1

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