Grabbag
What is buffering? How does the operating system do this?
A buffer is memory that stores a chunk of a file for reads and writes.
The OS buffers files into blocks, which are the smallest unit of the file that is read at a time.
What are the four main memory allocation functions, and what do they do?
malloc - allocates memory
calloc - allocates memory and clears it
realloc - reallocates memory
free - frees memory back to the OS
What are the steps of compilation (the entire process) in order?
(hint: there are five of them)
preprocessor, compiler, assembler, linker, loader,
To create an ADT, you need to use a ______ to define a name that is ____ to the client.
typedef, opaque
What is a system call? What is an example of a system call?
A system call is a function call made to the operating system.
Some examples are read, write (https://www.man7.org/linux/man-pages/man2/syscalls.2.html)
Allocate enough space for 30 elements for the variable x:
int * x;
x = (int*)malloc(sizeof(int) * 30);
Write a C-preprocessor macro which will give you sum of three numbers.
#define SUM(x,y,z) (x + y + z)
Define the user-accessible type for an ADT. It should be anonymous.
#ifnddef STACK_IMPLEMENTATION
typedef struct {} * ADT;
#endif
Write a C struct to define a binary tree, tree_node_s. A given node must store a string.
struct tree_node_s {
char * data;
struct tree_node_s * left;
struct tree_node_s * right;
};
Write a short code snippet that leaks 100 bytes of memory
int * x = malloc(100);
int * x = 0;
Place the following steps in the correct order: compiler, assembler, preprocessor, loader, linker. Explain briefly what occurs in each step.
Preprocessor: text replacement
Compiler: C code -> assembly code
Assembler: assembly code -> machine language code (object file)
Linker: object files -> executable
Loader: loads executable into memory
Explain the difference between Static and Dynamic typing, and give examples of languages that use them.
Static: checks types at compile time; C
Dynamic: checks types during execution, Python
What is the line of code to open a file called "test.txt" in order to read it?
FILE * file = fopen( "test.txt", "r" );
Write a code snippet that creates a dangling pointer.
int *x = malloc(sizeof(int) * 20);
int *y = x;
free(y);
// x is now a dangling pointer!
Define a macro that takes in a parameter (assumed to be a float) and prints both the name and value of the variable.
#define PRT(x) printf( #x “: %f\n”, x )
Explain the difference between a strongly and weakly typed language. Which category is C?
Strongly typed: can’t get around type restrictions
Weakly typed: can get around type restrictions
C is weakly typed (you can get around restrictions, ex: adding a pointer to an integer, casting, etc.)
What is the output of the code?
(1.png)
x1: 11
x2: 16
Draw a memory diagram for the following code. Separate the stack and heap.
int main() {
int a = 8;
int *a_ptr = malloc(sizeof(int));
int b = 10;
int *b_ptr = &b;
int **b_ptr_ptr = &b_ptr;
*a_ptr = 5;
return 0;
}
(img 2)
Define the following parts of just the compiler, and write what each produces.
Lexical analysis
Syntax analysis
Semantic analysis
Intermediate code generator
Lexical analysis: Breaks code into tokens
Syntax analysis: Creates a syntax tree from tokens
Semantic analysis: Checks correctness of syntax tree
Intermediate code generator: generates intermediate representation
Given the following struct used in a stack abstract data type, write a function, push_element, which adds an element to the top of the stack. If the stack is full, it should allocate more memory.
struct stack {
float * data;
long size;
long max_size;
}
typedef struct stack * StackADT;
void push_element( StackADT stack, float * num ) {
if( stack->size == stack->max_size ) {
float * temp = (float *) realloc( stack->data, stack->size * 2 );
assert( temp != NULL );
stack->data = temp;
stack->max_size *= 2;
}
stack->data[stack->size] = num;
stack->size++;
}