# C++ concepts: DefaultConstructible

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< cpp‎ | concept

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

### Requirements

The type `T` satisfies `DefaultConstructible` if

Given

- `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.
T() T{} | A temporary object of type `T` is value-initialized or aggregate-initialized.

### Notes

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`

### See also

is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11)(C++11)(C++11) | checks if a type has a default constructor (class template)

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