Dynamic memory in ANSI-C

Operators delete and new are sole of C++. They are not usable in the C language. But employing pure C language and its library, dynamic memory could also be employed via the functions calloc, malloc, free and realloc which are also usable in C++ comprising the <cstdlib> header file (see cstdlib for more info).

The memory blocks allocated by these functions are not inevitably compatible with those brought back by new, thus every one should be kept in line with its own set of operators and  functions.

Dynamic allcoation does not create/allocate space in STACK segment  while on the contrary as it in reality apportions in HEAP segment which is various from STACK. Every program has its own three memory segments, ie, code segment in which the composed code resides, stack segment in which the temporary  or local variables are laid in and heap segment which is employed for dynamic memory allotment. Stack is very volatile as it alters every function (or the code-block) comes in and expires. Meaning the variable produced throughout the function call is produced and demolished as the call expires. When the segment is not assigned an initial value to a computer program, it inclines to have the garbage data.

Where as the heap is for dynamic allotment by new()  or malloc() and keeps the data up to the allotment is authorized by delete() or  free().The allocated memory belongs to the pointer pointed-by up to it is freed/demolished or the main program ends. If the allocated memory is desolated by its pointer then it causes the memory leak, entailing the allocated memory is desolated (left ignored) and not permitting the similar to be recycled by other parts of the program. That is denoted as the memory leak.

Reallocate memory block

The size of the memory block pointed to by the ptr parameter is altered to size bytes, elaborating or reducing  quantity of memory usable in  block. The function might move the memory block to the new placement, in which event the new placement is brought back. The subject matter of the memory block is maintained up to the lesser of the old and new sizes, even if  block is motivated. If the new size is more prominent, the value of the newly allocated component is undetermined.

In event that ptr is NULL, the function acts exactly as malloc, attributing the new block of size bytes and bringing back the pointer to the offset of it.

In event that the size is 0, the memory antecedently allocated in ptr is deallocated as if the call to free was made, and the NULL pointer is brought back.

Parameters

ptr

ñ  Pointer to the memory block antecedently allocated with calloc,  realloc or malloc to be again allocated.

ñ  If this is NULL, the new block is allocated and the pointer to it is brought back by the function.

size

ñ  New size for  memory block, in the bytes.

ñ  If it is 0 and ptr points to the existent block of the memory,  memory block pointed by ptr is deallocated and  NULL pointer is brought back.

Return Value

ñ  A pointer to the again allocated memory block, which might be either the similar as the ptr argument or the new placement.

ñ  The sort of this pointer is void*, which could be cast to  coveted sort of data pointer in order to be the dereferenceable.

ñ  If the function broke down to allocate the called for block of memory, the NULL pointer is brought back, and the memory block pointed to by argument ptr is left unaltered.

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