Dynamic Memory Management

1. Dynamic Memory Management CAS CS210 Ying Ye Boston University

2. Program in Memory Taken from Likai Liu

3. Memory Allocation • Static memory allocation: • done at compile-time • allocated on stack • memory size known before compilation • freed automatically

4. Memory Allocation pushl %ebp movl %esp, %ebp subl $20, %esp leal 12(%ebp), %edx leal -8(%ebp), %ecx movl 8(%ebp), %eax movl %eax, 4(%esp) movl %edx, 8(%esp) movl %ecx, (%esp) call word_sum subl $4, %esp movl -4(%ebp), %eax imull -8(%ebp), %eax leave ret int prod(int x, int y) { str1 s1; str2 s2; s1.a = x; s1.p = &y; s2 = word_sum(s1); return s2.sum * s2.diff; }

5. Memory Allocation • Dynamic memory allocation: • done during run-time • allocated on heap • size of memory not necessarily known before compilation • freed manually

6. Memory Allocation #include <stdio.h> #include <stdlib.h> int main(void) { int size, *buf; scanf("%d", &size); buf = (int *)malloc(sizeof(int) * size); /* some other operations */ ...... free(buf); return 0; }

7. Linux Interface • void *malloc(size_t size); allocates size bytes and returns a pointer to the allocated memory, the memory is not initialized • void free(void *ptr); frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc • void *calloc(size_t nmemb, size_t size); • void *realloc(void *ptr, size_t size);

8. Download http://cs-people.bu.edu/yingy/alloc.c Allocate an integer array of size 5, store integers 1-5 in it, print them out in reverse order

9. buf = (int *)malloc(sizeof(int) * 5); int i; for(i = 0; i <5; i++) buf[i] = i + 1; for(i = 4; i >= 0; i--) printf("%d\n", buf[i]); free(buf);

10. Download http://cs-people.bu.edu/yingy/linkedlist.c Singly linked list implementation