21 #

Head First C Recap #

Memory Layout #

Know the memory layout well - it may come in handy later in this course.

At the very least, remember that the stack grows down and the heap grows up.

Arrays vs. Pointers #

Remember the differences between arrays and pointers - it can be really easy to make mistakes on this.

There are a few things you can do - one is to always use pointers in function parameters. Always prefer void foo(char* s) over void foo(char s[]).

You can turn on compiler warnings, which can helpfully point out potential errors. I use gcc -Wall -Wextra -pedantic ....

Think OS Recap #

A process represents an instance of a running program. This includes:

Program code
Data
Memory
Statuses (of I/O and network requests, etc.)
Hardware state

There are a lot of abstractions at play.

Processes can be interrupted and resumed by the OS. This gives the illusion of running multiple things simultaneously.
Each process thinks that it has access to all of the computer’s memory, but this is of course not the case.
On UNIX systems, everything is a file. Reading and writing on an input device, network card, or file is all the same abstraction.

Remember that you can run ps -e to see all running processes on your system. What is process number 1 for you?

Linux Tutorial #

For the next 20 minutes:

Head to the UNIX Tutorial for Beginners site: http://www.ee.surrey.ac.uk/Teaching/Unix/
Do Tutorials 4-6. After doing Tutorial 4, read the mangpage for puts.
If you don’t finish, try to do so before our next meeting.

Stack Diagrams #

For the next 10 minutes:

Draw a stack diagram for the following code, at the point just before increment finishes running for the first time.

void increment(int *p) {
    *p = *p + 1;
}

int add_and_increment(int *p, int *q) {
    int sum = *p + *q;
    increment(p);
    increment(q);
    return sum;
}

int main ()
{
    int x = 3;
    int y = 4;
    int sum = add_and_increment(&x, &y);
    printf("%d %d %d\n", x, y, sum);
}

For Next Time #

Finish Homework 2.
Read Chapter 2.5 of Head First C.
Finish the Linux Tutorials we covered today/