In the C++ programming language, the delete operator calls the destructor of the given argument, and returns memory allocated by new back to the heap[1]. A call to delete must be made for every call to new to avoid a memory leak. After calling delete the memory object pointed to is invalid and should no longer be used. Many programmers assign 0 (null pointer) to pointers after using delete to help minimize programming errors. Note, however, that deleting a null pointer has no effect (if the deallocation function is one supplied in the standard library[2]), so it is not necessary to check for a null pointer before calling delete.
Example code snippet:
int *p_var = 0; // new pointer declared p_var = new int; // memory dynamically allocated /* ....... other code ........*/ delete p_var; // memory freed up p_var = 0; // pointer changed to 0 (null pointer)
Arrays allocated with new [] can be similarly deallocated with delete []:
int size = 10; int *p_var = 0; // new pointer declared p_var = new int [size];// memory dynamically allocated /* ....... other code ........*/ delete [] p_var; // memory freed up p_var = 0; // pointer changed to 0
Arrays, allocated with new[], must be deallocated with delete[], since the layout of arrays, allocated with new[] is implementation defined, and possibly not compatible with new. For example, in order to properly perform object destruction at delete[], some implementations of new[] embed the number of allocated objects into the beginning of the allocated memory chunk, and return pointer to the remaining part of the array..
The delete operator (user defined) is different from operator delete. The delete operator may call operator delete to free up memory.
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