1. Dynamic Memory Allocation
Problem: Don't know how much memory to allocate to an array
Why?
Memory is allocated to the correct size for a record to be written to disk
Size depends upon a particular computer configuration
How? We use the C malloc and free functions

2. malloc() and free() void *malloc(size_t size) void free(void * data)
void * is a generic pointer for any type of data
size_t is a typedef for unsigned integers
allocates size in bytes
returns pointer to new memory or NULL
void free(void * data)
releases memory pointed to by data
If data is NULL, no harm done
C has no garbage collection, skipping free results in memory leaks
Prevent dangling references: set a pointer to NULL after free
Freeing from a function (pass a pointer to a pointer)
Function freeMyStructure( void **data) { free(*data); *data = NULL); }
Dangling reference: a pointer to dynamic memory that was released
Alias: Two pointers to the same dynamically allocated memory

3. Rules Never attempt to free memory twice
Never use a pointer after its memory was freed (dangling pointer)
Never attempt to free memory that wasn't allocated dynamically.
Set all pointers to null initially, and after freeing them

4. Example Static allocation: int nums[100;
Dynamic allocation int *nums, n; printf("How Many?\n"); scanf("%d", &n); nums = malloc(n * sizeof(int)); ••• free(nums); nums = NULL;
Note: sizeof is an operator that finds the byte length of a data type

5. Standard Programming Environment
Editors: vi, emacs, pico
Compiler: gcc or cc
Linker: gcc or cc
Automated system builder: make, ant
Profiler: gprof (find inefficient functions)
Source control system: SCCS, CVS
tracks code changes
coordinates changes among programmers
automatically assign release numbers

6. Hints for the last lab The file syntax is: model:year:rate\n
A sscanf %s will read the entire string up to a space. If none, it reads everything
Find the pointer to the colon, and store a NULL ('\0')
How to find the colon? Either a character by character search, or by using the C strstr method
You can then use sscanf on the back portion
'\0' F o r d : 9 8 . 5