Dynamic Memory Allocation

Question 1

Why are variable sized arrays problematic in C?

Answer 1

Not all versions of C support them

They are stored in the stack which has a limited amount of space

Question 2

Where are local variables and function parameters stored?

Answer 2

On the stack

Question 3

What is the heap used for?

Answer 3

Dynamic memory allocation at run time

Question 4

What argument does malloc take?

Answer 4

The number of bytes to reserve on the heap

Question 5

What does malloc return?

Answer 5

It returns a pointer to the memory space it has reserved

It returns a pointer of type void*

Question 6

Who is responsible for freeing memory that has been reserved using malloc?

Answer 6

The programmer

This is done using the free(pointer)

function

Question 7

Where are global variables stored?

Answer 7

In Static Data

Question 8

How is memory in the heap accessed?

Answer 8

It can only be accessed through pointers.

Question 9

How would we create a 2d int array that is of size AxB?

Answer 9

1. Create a pointer to an array of pointers.

int** 2d_arr = malloc(A * sizeof( int* ));

2. Assign a pointer to an int array to each element in the pointer array

for all pointers in the pointer array:

Question 10

What are two important things to remember when using malloc?

Answer 10

1. Always check that malloc hasn’t returned -1, indicating a failure
2. Remember to free the memory after it has been used, using the free(pointer) function