newis followed by a data type specifier and, if a sequence of more than one element is required, the number of these within brackets
. It returns a pointer to the beginning of the new block of memory allocated. Its syntax is:
pointer = new type
pointer = new type [number_of_elements]
type. The second one is used to allocate a block (an array) of elements of type
number_of_elementsis an integer value representing the amount of these. For example:
intand returns a pointer to the first element of the sequence, which is assigned to
foo(a pointer). Therefore,
foonow points to a valid block of memory with space for five elements of type
foois a pointer, and thus, the first element pointed to by
foocan be accessed either with the expression
fooor the expression
*foo(both are equivalent). The second element can be accessed either with
*(foo+1), and so on...
new. The most important difference is that the size of a regular array needs to be a constant expression, and thus its size has to be determined at the moment of designing the program, before it is run, whereas the dynamic memory allocation performed by
newallows to assign memory during runtime using any variable value as size.
neware going to be granted by the system.
bad_allocis thrown when the allocation fails. Exceptions are a powerful C++ feature explained later in these tutorials. But for now, you should know that if this exception is thrown and it is not handled by a specific handler, the program execution is terminated.
new, and is the one used in a declaration like:
nothrow, and what happens when it is used is that when a memory allocation fails, instead of throwing a
bad_allocexception or terminating the program, the pointer returned by
newis a null pointer, and the program continues its execution normally.
nothrow, declared in header
<new>, as argument for
foois a null pointer:
nothrowmethod is likely to produce less efficient code than exceptions, since it implies explicitly checking the pointer value returned after each and every allocation. Therefore, the exception mechanism is generally preferred, at least for critical allocations. Still, most of the coming examples will use the
nothrowmechanism due to its simplicity.
delete, whose syntax is:
new, and the second one releases the memory allocated for arrays of elements using new and a size in brackets (
deleteshall be either a pointer to a memory block previously allocated with
new, or a null pointer (in the case of a null pointer,
deleteproduces no effect).
How many numbers would you like to type? 5 Enter number : 75 Enter number : 436 Enter number : 1067 Enter number : 8 Enter number : 32 You have entered: 75, 436, 1067, 8, 32,
i), not a constant expression:
iso big that the system cannot allocate enough memory for it. For example, when I tried to give a value of 1 billion to the "How many numbers" question, my system could not allocate that much memory for the program, and I got the text message we prepared for this case (
Error: memory could not be allocated).
nothrow) or by catching the proper exception.
deletefor allocating dynamic memory. But these were not available in the C language; instead, it used a library solution, with the functions
free, defined in the header
<stdlib.h>in C). The functions are also available in C++ and can also be used to allocate and deallocate dynamic memory.
new, so they should not be mixed; each one should be handled with its own set of functions or operators.