Lecture 12 - Midterm 1 Review, malloc() and free() Flashcards
1
Q
include of complex numbers
A
- c has support for complex numbers
- # include <complex.h></complex.h>
2
Q
three types of complex numbers
A
- float complex
- double complex
- long double complex
3
Q
creal()
A
- typically used to extract the real part of the complex number
- A complex number is composed of the real and imaginary part
4
Q
cimag()
A
a function in C that extracts the imaginary part of a complex number with long double precision
5
Q
basic debugger (*nix)
A
- gdb is the roof of all UNIX degbuggers
- very useful in determining where the segmentation fault occurred, but not necessarily what caused it
6
Q
5 steps to use the basic debugger
A
$ gcc -g file.c -o file # -g flag important!
$ gdb file
(gdb) run (if problem, will stop at error line)
(gdb) bt (backtrace problem, can provide more info)
(gdb) quit
7
Q
precedence with structs
A
- it’s a little verbose to have to say (*p).x
- if the parentheses are omitted, the natural precedence is *(p.x) which means something really different
- wouldn’t it be nice if we had an operator that could be used to refer to a field within a structure pointed to by p
- it exists! p -> x
8
Q
NOTE ABOUT THE MIDTERM
A
know file I/O well, Turkstra specifically mentioned it in class
9
Q
structures containing pointers
A
- we mentioned several weeks ago that a structure can contain any definition (except a function)
- a pointer definition can be placed in a structure declaration
- in fact, we can define a pointer to the type of struct that we’re presently declaring
10
Q
what’s the point of structures containing pointers?
A
- not a lot of use creating a struct that points to itself
- however, if we have several structs that point to each other, it can create linked lists
11
Q
malloc()
A
- used for dynamic memory allocation
- reserves a block of memory on the heap an returns a pointer to the beginning of the block
- malloc(int size), size is size of memory block of bytes (use sizeof()!!)
- # include <malloc.h> !!</malloc.h>
12
Q
free()
A
- tells the system that we’re done with that chunk of memory
- free (address), address is where the memory you want to free is located
13
Q
calloc()
A
- calloc(int n, int s)
- reserves n chunks of memory of size s
- sets all of those bytes to 0
14
Q
dynamic memory
A
- memory layout usually starts with your functions, then global variables, and then local at the end
- so there’s a log of unused memory in the middle
15
Q
using memory in the middle of the dynamic memory shape
A
- called “the heap”
- don’t need to determine what addresses to use to store something, we have methods to do that
16
Q
things to remember with malloc() / free()
A
- when using malloc(), always double check that you specify the proper size
- always check the return value from malloc()
- after free(ptr), ptr still points to the same chunk of memory, but it’s not reserved
- always say ptr = NULL after a free(ptr) call so don’t try to use it again
17
Q
A
