Memory

Question 1

In general how does a stack work at initial run time?

Answer 1

Question 2

What is a stack frame/activation record and how/what information is stored?

Answer 2

It stores:

• parameters
• local variables
• return address

Question 3

How do array pointers work? How are they assigned and accessed?

Answer 3

1. Array pointers can point to the array name(and work like the original array)
2. Array pointers can point to an array’s index and that pointer would treat that as the 0 index and enumerate from there.

int a[5] = {10,20,30,40};

int* p1 = &a[1];

*p1 = 100; //(would change 20 to 100)

*p1[1] = 200; //(would change 30 to 200)

Question 4

Array’s do not know their own size, how can you determine the size of an array?

Answer 4

int a[17];

n = sizeof(a)/sizeof(a[0]);//would give size of array

Question 5

What is the heap?

Answer 5

• The heap is a large pool of unuesed memory that you canuse for dynamically allocating data
• it is allocated/deallocated explicity, not(like the stack) on function calls/returns

Question 6

How does malloc work? How is it initialized?

Answer 6

1. malloc function allocates a heap memory block of a given size

• returns a pointer to the first byte of memory
• can/should cast the returned point to the appropriate type
• initially the memory contains garbage data
• often use with sizeof to allocate memory for a given data type

2.

int* a[] = (int*)malloc(8 * (size of(int));

a[0] = 10;

a[1] = 20;

Question 7

What is calloc and how is it different from malloc? How do you initialize it?

Answer 7

• calloc is like malloc, but it zero’s out the memory(instead of leaving it)
• it also takes two parameters, number of elements and size of each
• it is preferred over malloc for avoiding bugs (but is slightly slower)

int* a = (int*)calloc(8, sizeof(int));

Question 8

How do you return a heap array using malloc?

Answer 8

int main(){

int nums[4] = {7,4,3,5};

}

int* copy(int a[], int size){

int i;

int* a2 = malloc(size * sizeof(int));

for(int i = 0; i< size; i++){

a2[i] = a[i];

}

return a2;

}

Question 9

How do you create a dynamically allocated string and array?

Answer 9

For String

char * p;

p = (char *) malloc(n+1);

For Array

int * a;

a = (int*)malloc(n * sizeof(int)); //n is whatever the size of the array would be.