C++ named requirements: DefaultConstructible

Specifies that an instance of the type can be default constructed.


The type T satisfies DefaultConstructible if.


  • u, an arbitrary identifier

The following expressions must be valid and have their specified effects.

Expression Post-conditions
T u; The object u is default-initialized
T u{}; The object u is value-initialized or aggregate-initialized.


A temporary object of type T is value-initialized or aggregate-initialized.


For objects of non-aggregate class type, a public default constructor must be defined (either user-defined or implicitly defined) to satisfy DefaultConstructible.

Non-const objects of non-class object type are always DefaultConstructible.

Const non-class types are not DefaultConstructible.

Const aggregate types are not DefaultConstructible if any of their members is an object of non-class type.

Non-object types (function types, reference types, and the (possibly cv-qualified) type void) as well as the const non-object types are never DefaultConstructible.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 724 C++98 the requirements of DefaultConstructible were missing added

See also

checks if a type has a default constructor
(class template)
specifies that an object of a type can be default constructed

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