Memory Allocation Flashcards
Why use dynamic memory allocation rather then just initializing like this, “ int variable[100]”
The arrays capacity might not be known till runtime, so it might be too much or to little capacity.
What is the stack?
changes size continually, out of programmers control
Can you manage the Heap? How?
Yes, referenced through pointers with the following library,
#include <stdlib.h>
void *malloc(size_t size);
void free(void * ptr);
void *calloc(size_t nmeb, size_t size);
void *realloc(void *ptr, size_t size);</stdlib.h>
In python what happens when objects are no longer referenced
garbage collection
what does malloc function do?
allocates a block of memory of specified size, from the heap, its uninitialized.
if memory cant be allocated with malloc, what is returned?
NULL (the null pointer value)
what does malloc return?
returns a pointer to the allocated block.
what does the free() function do?
deallocates the block of memory pointed to by ptr.
when will free() work?
only if the ptr is a pointer previously retuned by malloc
when will free do nothing?
when the pointer you are freeing is NULL
What are the objectives of the lecture on memory allocation?
The objectives include understanding the limitations of automatic memory allocation, explaining how program data is stored in computer memory, reviewing memory management in Python, and introducing C functions to handle dynamic memory.
In imperative programming languages, where are a function’s parameters and local variables typically allocated?
They are allocated in an activation frame, which is automatically created when the function is called and deallocated when the function returns.
How is memory allocated for local variables in Python?
In Python, a local variable is allocated the first time its name is bound to an object.
In C, when are parameters and local variables allocated?
Parameters and local variables whose scope is the entire function are allocated when the function is called.
What are automatic variables in the context of memory allocation?
Automatic variables are local variables in functions that are allocated and deallocated automatically when the function is called and returns, respectively.
What is the potential problem with the lifetime of automatic variables?
The values stored in automatic variables are not retained when the function where the variable is declared returns.
How does virtual memory work in computer systems?
Virtual memory allows the operating system to mimic non-existing memory blocks using a dedicated part of the hard drive, known as swap space or swap file.
What are the two main parts of virtual memory?
The two main parts are Kernel Space, where the OS kernel resides and is unavailable to processes, and User Space, where processes stay, work, and interact, each having its own sandbox and unable to access other sandboxes.
what should always be done after allocating memory with malloc?
use the assert function to verify that the pointer does not return NULL
What does assert function do?
terminates the program if the condition given in parameters does not return true
How to you allocate a struct?
typedef struct {
int x;
int y;
} point_t;
point_t *point;
point = malloc(sizeof(point_t));
assert(point != NULL);
what should you always do after freeing a block?
set the pointer that you freed to NULL, this will avoid any issues with free in the future regarding that specific block.
How do you allocate an array of 10 ints?
int *pa;
pa = malloc(10 * sizeof(int));
assert(pa != NULL);
// Access array elements by using []
// or pointer-plus-offset
pa[0] = 0; // *pa = 0;
*(pa + 1) = 0; // pa[1] = 0;
write a function that allocates an array of integers
with a specified capacity, and returns a pointer to the first
element
int *alloc_array_of_ints(int capacity){
int *pa;
assert(capacity > 0);
pa = malloc(capacity * sizeof(int));
assert(pa != NULL);
return pa;
}
