Example C Programs

I've written a bunch of short C programs to demonstrate how C programs interface with and use the Unix operating system. Here are links to them, in approximately the order in which I'll discuss them:

• cswap.c, which does the same job as the shell script swap: it takes two command-line arguments and prints them in reverse order.
• mycat.c, which does the same job as the "cat" command, at least in a simple form: with no arguments, it copies stdin to stdout, and with one argument, it copies the specified file to stdout.
• mycat2.c, a more general version that allows more than one file. It's also restructured to use a "dumpfile" function rather than doing the copying in-line.
• evalenv.c, which takes the name of an environment variable and prints out its value, if any.
• myset.c, which sets the value of an environment variable. Not a particularly useful program, since environment variables changed in a subprocess don't affect their values in the parent process.
• wsp.buggy.c. Several years ago I assigned people to write a program which would take an environment variable name and a filename, evaluate the environment variable as a colon-delimited list of directories (like PATH), and look for the specified filename in each of those directories. This is a BUGGY version of that program; I intentionally introduced some bugs to give people practice using gdb.
• clongword.c, which finds the longest word in stdin.
• clongword2.c, which also finds the longest word in stdin, but it uses scanf rather than reading character by character.
• clongword3.c, which does the exact same thing, but is a little more "bulletproof" in that it refuses to read a longer word than it has space for. Demonstrates use of sprintf.

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