7 Expressions [expr]

7.6 Compound expressions [expr.compound]

7.6.2 Unary expressions [expr.unary]

7.6.2.9 Delete [expr.delete]

1
#
The delete-expression operator destroys a most derived object or array created by a new-expression.
delete-expression:
:: delete cast-expression
:: delete [ ] cast-expression
The first alternative is a single-object delete expression, and the second is an array delete expression.
Whenever the delete keyword is immediately followed by empty square brackets, it shall be interpreted as the second alternative.64
If the operand is of class type, it is contextually implicitly converted ([conv]) to a pointer to object type.65
Otherwise, it shall be a prvalue of pointer to object type.
The delete-expression has type void.
2
#
If the operand has a class type, the operand is converted to a pointer type by calling the above-mentioned conversion function, and the converted operand is used in place of the original operand for the remainder of this subclause.
In a single-object delete expression, the value of the operand of delete may be a null pointer value, a pointer value that resulted from a previous non-array new-expression, or a pointer to a base class subobject of an object created by such a new-expression.
If not, the behavior is undefined.
In an array delete expression, the value of the operand of delete may be a null pointer value or a pointer value that resulted from a previous array new-expression whose allocation function was not a non-allocating form ([new.delete.placement]).66
If not, the behavior is undefined.
[Note 1: 
This means that the syntax of the delete-expression must match the type of the object allocated by new, not the syntax of the new-expression.
— end note]
[Note 2: 
A pointer to a const type can be the operand of a delete-expression; it is not necessary to cast away the constness ([expr.const.cast]) of the pointer expression before it is used as the operand of the delete-expression.
— end note]
3
#
In a single-object delete expression, if the static type of the object to be deleted is not similar ([conv.qual]) to its dynamic type and the selected deallocation function (see below) is not a destroying operator delete, the static type shall be a base class of the dynamic type of the object to be deleted and the static type shall have a virtual destructor or the behavior is undefined.
In an array delete expression, if the dynamic type of the object to be deleted is not similar to its static type, the behavior is undefined.
4
#
The cast-expression in a delete-expression shall be evaluated exactly once.
5
#
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.
6
#
If the value of the operand of the delete-expression is not a null pointer value and the selected deallocation function (see below) is not a destroying operator delete, evaluating the delete-expression invokes the destructor (if any) for the object or the elements of the array being deleted.
The destructor shall be accessible from the point where the delete-expression appears.
In the case of an array, the elements are destroyed in order of decreasing address (that is, in reverse order of the completion of their constructor; see [class.base.init]).
7
#
If the value of the operand of the delete-expression is not a null pointer value, then:
[Note 3: 
The deallocation function is called regardless of whether the destructor for the object or some element of the array throws an exception.
— end note]
If the value of the operand of the delete-expression is a null pointer value, it is unspecified whether a deallocation function will be called as described above.
8
#
If a deallocation function is called, it is operator delete for a single-object delete expression or operator delete[] for an array delete expression.
[Note 4: 
An implementation provides default definitions of the global deallocation functions ([new.delete.single], [new.delete.array]).
A C++ program can provide alternative definitions of these functions ([replacement.functions]), and/or class-specific versions ([class.free]).
— end note]
9
#
If the keyword delete in a delete-expression is not preceded by the unary ​::​ operator and the type of the operand is a pointer to a (possibly cv-qualified) class type T or (possibly multidimensional) array thereof:
  • (9.1)
    For a single-object delete expression, if the operand is a pointer to cv T and T has a virtual destructor, the deallocation function is the one selected at the point of definition of the dynamic type's virtual destructor ([class.dtor]).
  • (9.2)
    Otherwise, a search is performed for the deallocation function's name in the scope of T.
Otherwise, or if nothing is found, the deallocation function's name is looked up by searching for it in the global scope.
In any case, any declarations other than of usual deallocation functions ([basic.stc.dynamic.deallocation]) are discarded.
[Note 5: 
If only a placement deallocation function is found in a class, the program is ill-formed because the lookup set is empty ([basic.lookup]).
— end note]
10
#
The deallocation the function to be called is selected as follows:
  • (10.1)
    If any of the deallocation functions is a destroying operator delete, all deallocation functions that are not destroying operator deletes are eliminated from further consideration.
  • (10.2)
    If the type has new-extended alignment, a function with a parameter of type std​::​align_val_t is preferred; otherwise a function without such a parameter is preferred.
    If any preferred functions are found, all non-preferred functions are eliminated from further consideration.
  • (10.3)
    If exactly one function remains, that function is selected and the selection process terminates.
  • (10.4)
    If the deallocation functions belong to a class scope, the one without a parameter of type std​::​size_t is selected.
  • (10.5)
    If the type is complete and if, for an array delete expression only, the operand is a pointer to a class type with a non-trivial destructor or a (possibly multidimensional) array thereof, the function with a parameter of type std​::​size_t is selected.
  • (10.6)
    Otherwise, it is unspecified whether a deallocation function with a parameter of type std​::​size_t is selected.
Unless the deallocation function is selected at the point of definition of the dynamic type's virtual destructor, the selected deallocation function shall be accessible from the point where the delete-expression appears.
11
#
For a single-object delete expression, the deleted object is the object A pointed to by the operand if the static type of A does not have a virtual destructor, and the most-derived object of A otherwise.
[Note 6: 
If the deallocation function is not a destroying operator delete and the deleted object is not the most derived object in the former case, the behavior is undefined, as stated above.
— end note]
For an array delete expression, the deleted object is the array object.
When a delete-expression is executed, the selected deallocation function shall be called with the address of the deleted object in a single-object delete expression, or the address of the deleted object suitably adjusted for the array allocation overhead ([expr.new]) in an array delete expression, as its first argument.
[Note 7: 
Any cv-qualifiers in the type of the deleted object are ignored when forming this argument.
— end note]
If a destroying operator delete is used, an unspecified value is passed as the argument corresponding to the parameter of type std​::​destroying_delete_t.
If a deallocation function with a parameter of type std​::​align_val_t is used, the alignment of the type of the deleted object is passed as the corresponding argument.
If a deallocation function with a parameter of type std​::​size_t is used, the size of the deleted object in a single-object delete expression, or of the array plus allocation overhead in an array delete expression, is passed as the corresponding argument.
[Note 8: 
If this results in a call to a replaceable deallocation function, and either the first argument was not the result of a prior call to a replaceable allocation function or the second or third argument was not the corresponding argument in said call, the behavior is undefined ([new.delete.single], [new.delete.array]).
— end note]
64)64)
A lambda-expression with a lambda-introducer that consists of empty square brackets can follow the delete keyword if the lambda-expression is enclosed in parentheses.
65)65)
This implies that an object cannot be deleted using a pointer of type void* because void is not an object type.
66)66)
For nonzero-length arrays, this is the same as a pointer to the first element of the array created by that new-expression.
Zero-length arrays do not have a first element.