C Lab 3 C Arraylist Implementation

Goals ●Review ○ Referencing/Dereferencing ○ Free ●realloc and memmove ●ArrayList ●Debugging with GDB

Review: Pointer Syntax ●To get pointer to something, use ‘&’ ●‘&’ allows to pass items by reference ●To dereference or get item pointed to use ‘*’ ●‘*’ is the opposite of ‘&’

realloc ●realloc increases the size of memory allotted to pointer ●Arguments: pointer, amount of memory to allocate ●Returns a void* pointer to the reallocated memory ●Preserves data pointed to by original pointer ●Original pointer should be set to NULL, if space is found elsewhere

Realloc and Equivalent ptr = malloc(2); ptr = realloc(ptr, 1000); ptr = malloc(2); ptr2 = malloc(1000); memcpy(ptr2, ptr, 2); free(ptr); ptr = ptr2; ptr2 = NULL; Why not: ptr = malloc(2); realloc(ptr, 1000);

Review: free ●Remember to match each call to malloc with one call to free. int num = 3; free(&num); // :,O int *num = malloc(4) free(num); //yaaaayyy free(num); //staaahp

memmove ●Moves data from one memory address to another. ●Provide as arguments destination and source memory addresses, as well as the number of bytes to move. ●Syntax: memmove(dest_addr, source_addr, num_bytes);

C Arraylist Implemented as a struct with these fields: void** buffer; unsigned int buffer_size; unsigned int length; Buffer size and length are different! Recall: access struct fields with a.length, (a is a struct), or a->length, (a is a pointer to a struct).

C Arraylist Buffer size and length are different! Buffer size: The maximum number of elements the array list can hold, directly related to the amount of allocated memory. Length: The number of elements the array list actually holds. When the array list is full, expand it by doubling the amount of memory allocated for the buffer. Need to figure out how to detect this condition.

C Arraylist The arraylist is a list of pointers to memory locations. Therefore, the buffer variable is a pointer to a pointer (void** type) We use a void** pointer so that the arraylist can be used to store variables of any type.

GDB Gnu Project Debugger Tool used to find errors in your code. See C-lab 3 web page for basic commands.

#include Preprocessor directive to include a header file in your C code. Example: #include Performs textual inclusion (“copy-paste”). In practice, works like import statements in java, but there are some differences behind the scenes.

Debugging with GDB ●Begin the lab exercise ●Where/When might realloc be useful? ●Where/When might free be useful?