delete expression

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until C++17*)
noexcept specifier (C++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (C++11) auto (C++11)	constexpr (C++11) consteval (C++20) constinit (C++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (C++11)   Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (C++11)   final specifier (C++11)	explicit (C++11) static
Special member functions
Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

Expressions

General
Value categories Order of evaluation Constant expressions Primary expressions	Lambda expressions (C++11) Requires expressions (C++20) Pack indexing expression (C++26) Potentially-evaluated expressions
Literals
Integer literals Floating-point literals Boolean literals Character literals	Escape sequences String literals Null pointer literal (C++11) User-defined literal (C++11)
Operators
Assignment operators Increment and decrement Arithmetic operators Logical operators Comparison operators Member access operators Other operators new-expression delete-expression throw-expression	alignof sizeof sizeof... (C++11) typeid noexcept (C++11) Fold expressions (C++17) Alternative representations of operators Precedence and associativity Operator overloading Default comparisons (C++20)
Conversions
Implicit conversions Explicit conversions Usual arithmetic conversions     User-defined conversion	const_cast static_cast dynamic_cast reinterpret_cast

 

Destroys object(s) previously allocated by the new-expression and releases obtained memory area.

Syntax

::(optional) delete   expression	(1)
::(optional) delete[] expression	(2)

expression

-

one of the following: an expression of class type contextually implicitly convertible to a pointer to object type a prvalue of pointer to object type

1) Destroys one non-array object created by a new-expression.

2) Destroys an array created by a new[]-expression.

Explanation

Given the pointer evaluated from expression (after possible conversions) as ptr.

1) ptr must be one of

• a null pointer,
• a pointer to a non-array object created by a new-expression, or
• a pointer to a base subobject of a non-array object created by a new-expression.

The pointed-to type of ptr must be similar to the type of the object (or of a base subobject). If ptr is anything else, including if it is a pointer obtained by the array form of new-expression, the behavior is undefined.

2) ptr must be a null pointer or a pointer whose value is previously obtained by an array form of new-expression whose allocation function was not a non-allocating form (i.e. overload (10)).

The pointed-to type of ptr must be similar to the element type of the array object. If ptr is anything else, including if it is a pointer obtained by the non-array form of new-expression, the behavior is undefined.

The result of the delete-expression always has type void.

If the object being deleted has incomplete class type at the point of deletion, and the complete class has a non-trivial destructor or a deallocation function, the behavior is undefined(until C++26)the program is ill-formed(since C++26).

If ptr is not a null pointer and the deallocation function is not a destroying delete(since C++20), the delete-expression invokes the destructor (if any) for the object that is being destroyed, or for every element of the array being destroyed (proceeding from the last element to the first element of the array). The destructor must be accessible from the point where the delete-expression appears.

After that, whether or not an exception was thrown by any destructor, the delete-expression invokes the deallocation function: either operator delete (first version) or operator delete[] (second version), unless the matching new-expression was combined with another new-expression(since C++14).

The deallocation function's name is looked up in the scope of the dynamic type of the object pointed to by ptr, which means class-specific deallocation functions, if present, are found before the global ones. If :: is present in the delete-expression, only the global namespace is examined by this lookup. In any case, any declarations other than of usual deallocation functions are discarded.

If any deallocation function is found, the function to be called is selected as follows (see deallocation function for a more detailed description of these functions and their effects):

If at least one of the deallocation functions is a destroying delete, all non-destroying deletes are ignored.

(since C++20)

If the type's alignment requirement exceeds __STDCPP_DEFAULT_NEW_ALIGNMENT__, alignment-aware deallocation functions (with a parameter of type std::align_val_t) are preferred. For other types, the alignment-unaware deallocation functions (without a parameter of type std::align_val_t) are preferred. If more than one preferred functions are found, only preferred functions are considered in the next step. If no preferred functions are found, the non-preferred ones are considered in the next step. If only one function is left, that function is selected.

(since C++17)

• If the deallocation functions that were found are class-specific, size-unaware class-specific deallocation function (without a parameter of type std::size_t) is preferred over size-aware class-specific deallocation function (with a parameter of type std::size_t).

Otherwise, lookup reached global scope, and: If the type is complete and if, for the array form only, the operand is a pointer to a class type with a non-trivial destructor or a (possibly multi-dimensional) array thereof, the global size-aware global function (with a parameter of type std::size_t) is selected. Otherwise, it is unspecified whether the global size-aware deallocation function (with a parameter of type std::size_t) or the global size-unaware deallocation function (without a parameter of type std::size_t) is selected.

(since C++14)

The selected deallocation function must be accessible from the point where the delete-expression appears, unless the deallocation function is selected at the point of definition of the dynamic type’s virtual destructor.

The pointer to the block of storage to be reclaimed is passed to the deallocation function that was selected by the process above as the first argument. The size of the block is passed as the optional std::size_t argument. The alignment requirement is passed as the optional std::align_val_t argument.(since C++17)

If ptr is a null pointer value, no destructors are called, and the deallocation function may or may not be called (it's unspecified), but the default deallocation functions are guaranteed to do nothing when passed a null pointer.

If ptr is a pointer to a base class subobject of the object that was allocated with new, the destructor of the base class must be virtual, otherwise the behavior is undefined.

Notes

A pointer to void cannot be deleted because it is not a pointer to an object type.

Because a pair of brackets following the keyword delete is always interpreted as the array form of a delete-expression, a lambda-expression with an empty capture list immediately after delete must be enclosed in parentheses. // delete []{ return new int; }(); // parse error delete ([]{ return new int; })(); // OK

(since C++11)

Keywords

delete

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
CWG 288	C++98	for the first form, the static type of the operand was compared with its dynamic type	compare the static type of the object to be deleted with its dynamic type
CWG 353	C++98	whether the deallocation function will be invoked if the destructor throws an exception was unspecified	always invoked
CWG 599	C++98	the first form could take a null pointer of any type, including function pointers	except pointers to object types, all other pointer types are rejected
CWG 1642	C++98	expression could be a pointer lvalue	not allowed
CWG 2474	C++98	deleting a pointer to an object of a similar but different type resulted in undefined behavior	made well-defined
CWG 2624	C++98	pointers obtained from non-allocating operator new[] could be passed to delete[]	prohibited
CWG 2758	C++98	it was unclear how access control was done for the deallocation function and the destructor	made clear

See also

• new