delete-expression: ::opt delete cast-expression ::opt delete [ ] cast-expression
The first alternative is for non-array objects, and the second is for arrays. Whenever the delete keyword is immediately followed by empty square brackets, it shall be interpreted as the second alternative.79 The operand shall be of pointer to object type or of class type. If of class type, the operand is contextually implicitly converted (Clause [conv]) to a pointer to object type.80 The delete-expression's result has type void.
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 section. In the first alternative (delete object), the value of the operand of delete may be a null pointer value, a pointer to a non-array object created by a previous new-expression, or a pointer to a subobject ([intro.object]) representing a base class of such an object (Clause [class.derived]). If not, the behavior is undefined. In the second alternative (delete array), 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.81 If not, the behavior is undefined. [ Note: 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: 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 ]
In the first alternative (delete object), if the static type of the object to be deleted is different from its dynamic type, 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 the second alternative (delete array) if the dynamic type of the object to be deleted differs from its static type, the behavior is undefined.
If the value of the operand of the delete-expression is not a null pointer value, the delete-expression will invoke the destructor (if any) for the object or the elements of the array being deleted. In the case of an array, the elements will be destroyed in order of decreasing address (that is, in reverse order of the completion of their constructor; see [class.base.init]).
If the value of the operand of the delete-expression is not a null pointer value, then:
If the allocation call for the new-expression for the object to be deleted was not omitted and the allocation was not extended ([expr.new]), the delete-expression shall call a deallocation function ([basic.stc.dynamic.deallocation]). The value returned from the allocation call of the new-expression shall be passed as the first argument to the deallocation function.
Otherwise, if the allocation was extended or was provided by extending the allocation of another new-expression, and the delete-expression for every other pointer value produced by a new-expression that had storage provided by the extended new-expression has been evaluated, the delete-expression shall call a deallocation function. The value returned from the allocation call of the extended new-expression shall be passed as the first argument to the deallocation function.
Otherwise, it is unspecified whether the deallocation function will be called. [ Note: The deallocation function is called regardless of whether the destructor for the object or some element of the array throws an exception. — end note ]
[ Note: An implementation provides default definitions of the global deallocation functions operator delete() for non-arrays ([new.delete.single]) and operator delete() for arrays ([new.delete.array]). A C++ program can provide alternative definitions of these functions ([replacement.functions]), and/or class-specific versions ([class.free]). — end note ]
When the keyword delete in a delete-expression is preceded by the unary :: operator, the deallocation function's name is looked up in global scope. Otherwise, the lookup considers class-specific deallocation functions ([class.free]). If no class-specific deallocation function is found, the deallocation function's name is looked up in global scope.
If the type is complete and if deallocation function lookup finds both a usual deallocation function with only a pointer parameter and a usual deallocation function with both a pointer parameter and a size parameter, then the selected deallocation function shall be the one with two parameters. Otherwise, the selected deallocation function shall be the function with one parameter.
When a delete-expression is executed, the selected deallocation function shall be called with the address of the block of storage to be reclaimed as its first argument and (if the two-parameter deallocation function is used) the size of the block as its second argument.82
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.
This implies that an object cannot be deleted using a pointer of type void* because void is not an object type.
For non-zero-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.
If the static type of the object to be deleted is complete and is different from the dynamic type, and the destructor is not virtual, the size might be incorrect, but that case is already undefined, as stated above.