Lecture 15

March 15, 2019

For today:

1) Read HFC Chapter 7

2) Finish Homework 6

3) Plan the end game of your project

Today:

1) const

2) Semaphores continued

3) HFC Chapter 7

4) Project time

For next time:

1) Read Think OS Chapter 7 and do the reading quiz

2) Prepare for a quiz

Project 1 due the evening of March 26

Const

Read this article about the Const Qualifier in C

Benefits:

1) Declaring things const allows you to catch errors.

2) And it allows the compiler to do some optimizations.

But it is not a security feature that prevents abuse; it might save you from errors, but it is easy to subvert.

It's like putting an alarm on the refrigerator, not a lock.

Also, declaring a pointer to a structure const means that you cannot modify the struct using that pointer.  But it does not make the struct itself immutable; you could still modify it using another pointer.

HFC Chapter 7

Good page to review:

My recommendation: Use fgets to get strings and do basic error checking.

Then parse the input as a separate step, possibly using sscanf.

Learning to use pointers to functions

Step 1: Use a library function, like qsort, that takes a function as a parameter.

Step 2: Write a function that takes a function as a pointer.  The concept is simple, but the syntax is unpleasant.

Step 3: Profit.

This page might help: http://www.unixwiz.net/techtips/reading-cdecl.html

And you might want to bookmark this one: http://cdecl.org/

Try these examples from the book: 

int (*match)(char*)

char** (*names_fn)(char*, int)

int (*compar)(const void *, const void *)

void (*qsort)(void *, 

              size_t, 

              size_t, 

              int (*compar)(const void *, const void *))

Note: the last one is correct, but seems to break cdecl.org!

See if you can figure out this one: char *(*(**foo[][8])())[]

Then use cdecl.org to check.

Finally, let's do the exercises on page 328 and 329 of HFC.