malloc(): It is a C library function that can also be used in C++, while the “new” operator is specific for C++ only. Both malloc() and new are used to allocate the memory dynamically in heap. But “new” does call the constructor of a class whereas “malloc()” does not.
The function malloc() is used to allocate the requested size of bytes and it returns a pointer to the first byte of allocated memory. It returns null pointer, if fails. The function free() is used to deallocate the allocated memory by malloc().
delete and free() in C++ In C++, the delete operator should only be used either for the pointers pointing to the memory allocated using new operator or for a NULL pointer, and free() should only be used either for the pointers pointing to the memory allocated using malloc() or for a NULL pointer. It is an operator.
Dynamic memory allocation This helps us avoid running into insufficient memory and makes us use the memory space efficiently. In the C programming language, two of the functions used to allocate and deallocate the memory during run-time are malloc() and free() , respectively.
new
/ delete
new
(standard version) never returns a NULL
(will throw on failure).malloc
/ free
is implementation defined.std::set_new_handler
).operator new
/ operator delete
can be overridden legally.malloc
/ free
void*
.NULL
on failure.new
/ delete
.malloc
/ free
can NOT be overridden legally.Feature |
new / delete
|
malloc / free
|
---|---|---|
Memory allocated from | 'Free Store' | 'Heap' |
Returns | Fully typed pointer | void* |
On failure | Throws (never returns NULL ) |
Returns NULL
|
Required size | Calculated by compiler | Must be specified in bytes |
Handling arrays | Has an explicit version | Requires manual calculations |
Reallocating | Not handled intuitively | Simple (no copy constructor) |
Call of reverse | Implementation defined | No |
Low memory cases | Can add a new memory allocator | Not handled by user code |
Overridable | Yes | No |
Use of constructor / destructor | Yes | No |
Technically, memory allocated by new
comes from the 'Free Store' while memory allocated by malloc
comes from the 'Heap'. Whether these two areas are the same is an implementation detail, which is another reason that malloc
and new
cannot be mixed.
The most relevant difference is that the new
operator allocates memory then calls the constructor, and delete
calls the destructor then deallocates the memory.
new
calls the ctor of the object, delete
call the dtor.
malloc
& free
just allocate and release raw memory.
new
/delete
is C++, malloc
/free
comes from good old C.
In C++, new
calls an objects constructor and delete
calls the destructor.
malloc
and free
, coming from the dark ages before OO, only allocate and free the memory, without executing any code of the object.
In C++ new
/delete
call the Constructor/Destructor accordingly.
malloc
/free
simply allocate memory from the heap. new
/delete
allocate memory as well.
The only similarities are that malloc
/new
both return a pointer which addresses some memory on the heap, and they both guarantee that once such a block of memory has been returned, it won't be returned again unless you free/delete it first. That is, they both "allocate" memory.
However, new
/delete
perform arbitrary other work in addition, via constructors, destructors and operator overloading. malloc
/free
only ever allocate and free memory.
In fact, new
is sufficiently customisable that it doesn't necessarily return memory from the heap, or even allocate memory at all. However the default new
does.
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