Transcript Dynamic Memory Allocation

Dynamic Storage Allocation
CS362
Dynamic Storage Allocation
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Needed understanding of the amount of data to be stored.
For example: amount of data required to size an array.
If not known, best guess, not the best situation.
As program executes “dynamic (runtime) memory” is
allocated (otherwise known as the heap)
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Static Memory – allocated during the compilation of the program
Dynamic Memory – allocated during the execution of the program
We can access the dynamic memory via pointers
Dynamic Memory Allocation
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To create dynamic variables we use the “new” operator
“new” allocates either:
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one storage cell and returns a pointer to the cell
a series of contiguous storage cells (an array) and returns a pointer
to the first cell (dynamic array)
For example:
int *ptr, *iptr;
ptr = new int;
// pointer to a single integer in dynamic memory
or
iptr = new int[size]; // pointer to a dynamic array of integer, this is
// an anonymous array and can only be accessed
// via pointers
Dynamic Memory Allocation
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Programs often use memory on a temporary basis.
Memory no longer required should be de-allocated.
De-allocation returns memory to the heap.
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Which means it can be re-used.
Memory is de-allocated using the “delete” operator
“delete” returns the space allocated by “new”
For example:
delete ptr;
or
delete [ ] iptr;
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// deallocated single memory location
// deallocates the entire array
Pointers still exist, but do not point to anything.
Dynamic Memory Allocation
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After de-allocating memory, the pointer still points at the
same memory location, but it is now inaccessible
A pointer without a valid value is a “dangling pointer”
An attempt to access the memory may crash the program
Eliminate this issue by setting the pointer variable to NULL