Memory management

Add dynamic memory management with malloc and free.

Dynamic Book with malloc

Instead of a fixed array, you can allocate a Book at runtime with malloc. This lets the catalog size be set dynamically.

struct Book *b = malloc(sizeof(struct Book));
strcpy(b->title, "Suç ve Ceza");
b->year = 1866;
free(b);

Here b is a pointer; it points to the Book on the heap. You access members with the -> operator (not dot). When done, you give the memory back with free. This is the basis of dynamic catalogs.

Assigning the title with strcpy

You cannot assign directly to a char array; you copy characters with strcpy. The <string.h> header is required.

strcpy(b->title, "Suç ve Ceza");
b->year = 1866;

Here strcpy copies the second string into the first. year is an int so it can be assigned directly with =. This difference comes from C treating string and integer assignments differently.

Exercise Allocate a Book with malloc and print

Add the <stdlib.h> and <string.h> headers. Allocate a Book with malloc(sizeof(struct Book)); set the title to "War and Peace" with strcpy; assign b->year = 1869. Print with print_book(*b); release with free(b).

Show example solution

#include <stdlib.h>
#include <string.h>
struct Book *b = malloc(sizeof(struct Book));
strcpy(b->title, "War and Peace");
b->year = 1869;
print_book(*b);
free(b);

Test yourself

Fill in the blank: pointer member access
```
b____ = 1866;
```
Show answer
```
b->year = 1866;
```
Match expression to meaning

b->title

Title member
b->year

Year member
malloc

Allocates on heap
free

Releases heap
Which function is called to release a Book allocated with malloc?
- delete
- release
- free
- destroy
Show answer

free — free gives back heap memory allocated with malloc.

Next lesson: Putting it together

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