C/C++ Basic-- the differs between [malloc&free] and [new &delete]

1.basic concepts

malloc&free and new&delete are all used to request memory allocation and release memory allocated from heap area.

eg.

malloc.h must be referenced when using malloc&free

i)

int *array;

array=(int *)malloc(4*sizeof(int));// declare an array which has four int elements

....

free(array);//release the memory which is allocated to array.

ii)

int *array

array=new int[4];

...

delete[] array;

all these two cases works the same. but what is their differs then? are they the same functioanlity? NO!

2.diffs.

we can only say that in some cases, they work the same.that is to say, we can use malloc&free to take place of new&delete. but this can not applied all the time.

the main reason is :malloc will not invoke class construtor in C++, while new do. At the same time, free will not invoke destructor,while delete do.

eg.

class TDate

{

public:

TDate()

{

month=1;

day=1;

year=1;

printf("constructor is invoked");

}

~TDate()

{

printf("destructor is invoked");

}

protected:

int month;

int day;

int year;

}

case 1: use Malloc

TDate *p;

p=(TDate *)malloc(sizeof(TDate));//do not invoke constructor at all

...

free(p);//do not invoke destructor at all

in this case, the constructor of TDate will not be invoked. so all its memebers can not be initialized.



case 2: use new

TDate *p;

p=new Tdate;//invoke constructor to initialize the instance

...

delete p;//invoke destructor to release resource.