CODEWITHSUNDEEP
c++initializationlanguage-lawyer
chenzhongpu
chenzhongpu

Reputation: 6871

Are dynamically allocated objects default initialized?

In C++ Primer 5th (chapter 12),

By default, dynamically allocated objects are default initialized, which means that objects of built-in or compound type have undefined value;

int *pi = new int; // unitialized int

This statement indicates that built-in type object has undefined value when default initialized. However, the behaviour of default initialized built-in type object depends on where it is defined.

To be specific, built-in type object outside any function shall be 0, while built-in type object inside some block has undefined value.

Hence, I think the statement above is not accurate，since for built-in type:

default initialized != undefined value

Do I understand this properly?

Upvotes: 3

Views: 168

Answers (1)

Brian Bi
Brian Bi

Reputation: 119134

For non-class types, default initialization performs no initialization.

However, variables with static or thread storage duration are always zero-initialized before any other initialization takes place. So if you have int x; at the global scope, although the default initialization does nothing, x is still initialized to zero due to the zero-initialization that takes place before the default initialization.

For a non-class object with dynamic storage duration, if no initializer is given, the value is indeterminate because zero-initialization does not apply.

Upvotes: 8

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