CS631 -- Advanced Programming in the UNIX Environment

File Descriptors Warmup Exercise

Write a small program that:

• prints the value of the STDIN_FILENO, STDOUT_FILENO, and STDERR_FILENO constants
• prints the value of the file descriptors referenced via the stdin, stdout, and stderr streams
• open(2)s a file, then prints the value of the resulting file descriptor
• fopen(3)s a file, then prints the value of the file descriptor referenced via that stream

What happens when you open the same file multiple times with or without closing it again in between?

Try opening the same file twice, then writing different data to each file descriptor (via write(2)) - what happens?

Open an existing file that contains some data - perform alternate read(2) and write(2)s on that file descriptor. What does that tell you about the position in the file as you perform these operations? How would you go about replacing a specific word in a file?

Even for this warmup exercise, remember to ensure that your code complies with our requirements (style, checklist, general guidelines).