New and malloc

new and malloc difference （8 individual ）
（1）new and delete yes C++ Key words of / Operator ,malloc And free yes c++/c The standard function of language .

（2）malloc You need to explicitly specify the allocated memory size ,new Unwanted .
class A{…}
A * ptr = new A;
A * ptr = (A *)malloc(sizeof(A)); // You need to explicitly specify the required memory size sizeof(A);

（3）new The operator dynamically allocates memory space for objects from free storage , and malloc Function dynamically allocates memory from the heap . Free storage is C++ be based on new An abstract concept of an operator , Usually through new Operator for memory request , This memory is the free storage area . And heap is an operating system term , It is a special memory maintained by the operating system , For dynamic allocation of program memory ,C Language use malloc Allocate memory from the heap , Use free Release the allocated memory . So can a free storage area be a heap （ The problem is equivalent to new Whether memory can be allocated dynamically on the heap ）, It depends. operator new Implementation details . Free storage can be more than just a heap , It can also be static storage , It's all up to you operator new Where to allocate memory for objects

（4）new When operator memory allocation succeeds , Return object type , No type conversion required , so new Is a type safe operator ;malloc return void*, You need to cast void* The pointer is converted to the type we need .

（5）new When the operator memory allocation fails , Throw out bad_alloc abnormal ;malloc Return when memory allocation fails NULL.

（6）new Operators have constructors and destructors , While opening up space , The constructor of the custom object will be called to complete the initialization ;malloc It will only open up space .

（7）malloc After allocating space , Can pass realloc Expand memory ;new Operator cannot expand memory again .

（8）new relative malloc Low efficiency , because new The bottom layer encapsulates malloc.