Lab 11 -- Advanced Pointers and Callbacks

In this, your final lab assignment, you will learn about some of the more advanced usage of C's pointers, and a few other items of importance that did not make it into previous labs.

There are a number of Unix commands or options to commands that are well worth knowing about that have not come up so far. Here are a few to experiment with:

Question 1: Give a brief description of each command above. Tip: try strings on one of your executables generated from compiling and linking a C program. (10 points)

We have seen that you can retrieve the command line parameters to a program through the argc and argv parameters to your program's main function. You might have noticed that many of the Unix commands you've learned about this semester make heavy use of command-line parameters. These often are switches that start with - or --. For example, see the man page for ls. You can imagine that simply parsing the command line parameters to decide what the command is supposed to do can be a complex task.

The C standard library provides a mechanism to parse these command-line parameters more easily and efficiently: getopt. See the description in section 3 of the manual: getopt(3).

Practice Program: Add three new command-line options to this program. One is a required parameter specifying the name of an output file, to be specified with -o or -output-file. The second is a flag that would turn on a "debug mode" in the program by setting a variable debug to 1 (its default should be 0 if the flag is not specified), to be specified with -d or -debug. The last is a number which represents the enrollment in a class, is required, and must be positive, to be specified with the -e or -enrollment flags. (10 points)

Section 5.11 of K&R shows you a way you can write a sort function to sort data in multiple ways by specifying a function pointer as one of the parameters to the sort function. In this case, this would be a comparator function that knows how to compare two values during the swap procedure. This idea is formalized in Java with the Compatator interface, but as usual, in C, we can achieve similar functionality but without the formal language or API support.

Make sure you understand how this works, then look at the qsort function provided by the C standard library (man qsort). This works similarly to the one in K&R, but works on an arbitrary array of any data type.

Practice Program: Add functionality to the above example. Your program should be able to sort floating point values either in ascending or descending order, and should introduce the ability to read in and sort at least one new data type (a struct that holds some non-trivial data) by at least two different criteria. (15 points)

For another way to use function pointers in a way somewhat like an iterator, see the function sll_visit_all and its usage in the previous example:

Practice Program: Add a callback function find_max and a call to sll_visit_all that demonstrates its use to the slltest.c program in the above example. (5 points)

Please submit all required files as email attachments to terescoj AT strose.edu. You are recommended to do so by Thursday, January 16, 2014. Be sure to check that you have used the correct file names and that your submission matches all of the submission guidelines listed on the course home page.

Grading Breakdown
Lab question	10 points
`getopt` enhancement	10 points
`qsort` enhancement	15 points
`find_max` enhancement	5 points