CS 330 Lecture 15 – Malloc
Agenda
- preprocessor macros
- memory leaks
- adjusting an allocation with realloc
- how malloc works, kinda
- p1 = malloc(4 * sizeof(int))
- p2 = malloc(5 * sizeof(int))
- p3 = malloc(6 * sizeof(int))
- free(p2)
- p4 = malloc(2 * sizeof(int))
TODO
- For more background on malloc, browse http://www.gnu.org/software/libc/manual/html_node/Memory-Allocation.html#Memory-Allocation.
- Read http://en.wikibooks.org/wiki/X86_Assembly/GAS_Syntax.
Code
makefile
EXES = first arrays months oob strings test_stack all: $(EXES) $(EXES): %: %.c stack.h stack.c gcc -o $@ -Wall -g -std=c99 $< stack.c clean: rm -f $(EXES)
stack.h
#ifndef STACK_H
#define STACK_H
const int ESTACK_UNDERFLOW;
struct stack_t {
int *elements;
int top;
};
struct stack_t *make_stack(int nelements);
// Add element to stack
void push(struct stack_t *stack, int new_thing);
int pop(struct stack_t *stack);
int peek(const struct stack_t *stack);
void free_stack(struct stack_t *stack);
#endif
stack.c
#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include "stack.h"
#define EZMALLOC(type, nelements) \
(type *) malloc(nelements * sizeof(type))
const int ESTACK_UNDERFLOW = 10982;
/* ------------------------------------------------------------------------- */
struct stack_t *make_stack(int nelements) {
/* struct stack_t *new_stack = (struct stack_t *) malloc(sizeof(struct stack_t)); */
struct stack_t *new_stack = EZMALLOC(struct stack_t, 1);
/* new_stack->elements = (int *) malloc(sizeof(int) * nelements); */
new_stack->elements = EZMALLOC(int, nelements);
new_stack->top = 0;
return new_stack;
}
/* ------------------------------------------------------------------------- */
int peek(const struct stack_t *stack) {
/* assert(stack->top > 0); */
errno = ESTACK_UNDERFLOW;
return stack->elements[stack->top - 1];
}
/* ------------------------------------------------------------------------- */
int pop(struct stack_t *stack) {
/* assert(stack->top > 0); */
errno = ESTACK_UNDERFLOW;
--stack->top;
return stack->elements[stack->top];
}
/* ------------------------------------------------------------------------- */
void push(struct stack_t *stack, int new_thing) {
stack->elements[stack->top] = new_thing;
stack->top++;
}
/* ------------------------------------------------------------------------- */
void free_stack(struct stack_t *stack) {
free(stack->elements);
free(stack);
}
/* ------------------------------------------------------------------------- */
test_stack.c
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "stack.h"
#include "foo.h"
int main(int argc, char **argv) {
struct stack_t *operands = make_stack(100);
for (int i = 0; i < argc; ++i) {
if (isdigit(argv[i][0])) {
push(operands, atoi(argv[i]));
} else if (strcmp(argv[i], "*") == 0) {
int b = pop(operands);
int a = pop(operands);
push(operands, a * b);
} else if (strcmp(argv[i], "+") == 0) {
int b = pop(operands);
int a = pop(operands);
push(operands, a + b);
}
}
printf("%d\n", pop(operands));
free_stack(operands);
/* push(operands, 10); */
/* push(operands, 13); */
/* push(operands, 17); */
/* for (int i = 0; i < 3; ++i) { */
/* printf("pop(operands): %d\n", pop(operands)); */
/* } */
return 0;
}
Haiku
I’m glad I am young.
All the blech problems are solved.
What next? World peace.
All the blech problems are solved.
What next? World peace.