Question

When I use new [] to apply memory. In the end, I use delete to free memory (not delete[]). Will this cause memory leak?

Two types:

1. Builtin types, like int, char, double …
   I am not sure.
2. class types.

I think may free leak. because the destruct function.

Many people and some books tell me, new[] -> delete[] ; new -> delete.

I want to know why.
so I check vs2010 source code, it must be use memory pool mechanism. It is long and complex . I can’t continue read.

How are delete and delete[] implemented?

Answer 1

When I use new [] to apply memory. In end , I use delete to free memeory(not delete[]).Must be memory leak ?

If you use new[], and then delete (not delete[]), then according to the langauge specification, it invokes undefined-behavior which means anything could happen. It may cause memory leak or may not. No such guarantee is given by the language, nor by the compiler.

Many people and some books tell me, new[]->delete[]; new->delete . I want to know why ?

Short answer : because the specification says so.

Long answer: the functions which implementnew and new[] are implemented differently: new assumes memory of one item is to be allocated, while new[] assumes memory of n item is to be allocated where n is passed to the function as argument. So to undo the process (i.e to deallocate the memory), there should be two functions as well : delete and delete[] which are implemented differently, each makes some assumption about the memory allocated by their counterparts. For example, delete simply assumes memory allocated for one item is to be deallocated; on the other hand delete[] needs to know the number of items for which memory is to be deallocated, so it assumes that new[] stores the number of items somewhere in the allocated memory, most commonly in the begginning of the allocated memory, and so delete[] first reads that portion of memory which stores the number of items, and then deallocates the memory, accordingly.

Note that new and new[] each calls the default constructor to construct the object(s) in the allocated memory, and delete and delete[] calls the destructor to destruct the object before deallocating the memory.