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malloc returns void pointer
new returns the pointer to the object that is created (eg: A *a = new A(); returns pointer of type A)

malloc does not call constructor
new calls constructor

I got the same question on my interview. First answer is that malloc is allocation method from C and new is allocation method from C++. There is no object-oriented programming in C, and therefore malloc don't know about constructors. So the basic answer is that new allocates memory and calls the constructor, where malloc only allocates memory and return pointer on the void* without any values initalized (we have to memset them to 0). I also mentioned that malloc and new use different allocation techniques so we shouldn't use malloc with delete and new with free.

@Kozikowski: You are correct. One more difference is there.

malloc always returns 0 (or NULL) when it runs out of memory. but new used to do this until Microsoft Visual Studio 6.0 but after C++03 standard (came in 2003, latest so far, C++0x is about to come!) and in later compiler's new NEVER EVER returns 0 or NULL, it always throws std::bad_alloc exception if it runs out of memory, however you can still change this behavior to old (returning 0) behavior by using this syntax!

int *p = new(nothrow) int;

if memory cant b allocated...malloc returns NULL
if memory cant b allocated...new throws exception

Two more :

1. new can be overloaded, malloc doesn't know what overloading is :)
2. new doesn't require you to specify size of mem to be allocated, malloc cannot work without it.

Two more :

1. new can be overloaded, malloc doesn't know what overloading is :)
2. new doesn't require you to specify size of mem to be allocated, malloc cannot work without it.

thank you all for the answers

new returns correct type of pointer
while malloc returns void*


new automatically calculates the size of memory to be allocated while in malloc we have tp pass the size of memory to be allocated

new is an operator in c++ while malloc is a function

new returns correct type of pointer
while malloc returns void*


new automatically calculates the size of memory to be allocated while in malloc we have tp pass the size of memory to be allocated

new is an operator in c++ while malloc is a function