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What is diff between malloc()/free()
and new/delete?
malloc allocates memory for object in heap but doesn't invoke
object's constructor to initiallize the object.
new allocates memory and also invokes constructor to initialize
the object.
malloc() and free() do not support object semantics
Does not construct and destruct objects
string * ptr = (string *)(malloc (sizeof(string)))
Are not safe
Does not calculate the size of the objects that it construct
Returns a pointer to void
int *p = (int *) (malloc(sizeof(int)));
int *p = new int;
Are not extensible
new and delete can be overloaded in a class
"delete" first calls the object's termination routine (i.e. its
destructor) and then releases the space the object occupied on
the heap memory. If an array of objects was created using new,
then delete must be told that it is dealing with an array by
preceding the name with an empty []:-
Int_t *my_ints = new Int_t[10];
...
delete []my_ints;
What is the diff between "new" and "operator new" ?
"operator new" works like malloc.
What is difference between template and macro??
There is no way for the compiler to verify that the macro
parameters are of compatible types. The macro is expanded
without any special type checking.
If macro parameter has a postincremented variable ( like c++ ),
the increment is performed two times.
Because macros are expanded by the preprocessor, compiler error
messages will refer to the expanded macro, rather than the macro
definition itself. Also, the macro will show up in expanded form
during debugging.
for example:
Macro:
#define min(i, j) (i < j ? i : j)
template:
template<class T>
T min (T i, T j)
{
return i < j ? i : j;
}
What are C++ storage classes?
auto
register
static
extern
auto: the default. Variables are automatically created and
initialized when they are defined and are destroyed at the end
of the block containing their definition. They are not visible
outside that block
register: a type of auto variable. a suggestion to the compiler
to use a CPU register for performance
static: a variable that is known only in the function that
contains its definition but is never destroyed and retains its
value between calls to that function. It exists from the time
the program begins execution
extern: a static variable whose definition and placement is
determined when all object and library modules are combined
(linked) to form the executable code file. It can be visible
outside the file where it is defined. |
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