delete (C++)

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 = NULL;  // new pointer declaredp_var = new int; // memory dynamically allocated /* .......other code........*/ delete p_var;   // memory freed upp_var = NULL;   // pointer changed to 0 (null pointer)

Arrays allocated with new [] can be similarly deallocated with delete []:

int size = 10;int *p_var = NULL;   // new pointer declaredp_var = new int [size];  // memory dynamically allocated /* .......other code........*/ delete [] p_var; // memory freed upp_var = NULL; // pointer changed to 0

Arrays, allocated with new[], must be deallocated with delete[], since the layout of arrays, allocated with new[] is implementation defined,^{[citation needed]} 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.^{[citation needed]}

The delete operator (user defined) is different from operator delete. The delete operator may call operator delete to free up memory.

See also

• New (C++)
• Resource Acquisition Is Initialization (RAII)

References

External links

• Attacking delete and delete [] in C++