Laurence Tratt: How can C Programs be so Reliable?

http://tratt.net/laurie/tech_articles/articles/how_can_c_programs_be_so_reliable

by swah • 15 years ago

15 2 15 years ago

derleth• 15 years ago

First: Pointers do have a simple real-world analogy. They're post office box numbers.

A given post office box is a container with a fixed size and a fixed number. You can refer to a post office box using that number. You can also do things like say "Get me everything from the four post office boxes beginning with post office box 20." or "Go to post office box 3, go down two boxes, and get me what's in the post office box there."

Finally, you can write a post office box number down and stick it into a different post office box. Then, to get anything useful, you have to say things like "Go to post office box 15, open it and read the piece of paper inside, go to the post office box with the same number as the one written on the piece of paper you just read, and get me what's in that box." You can actually 'chain' requests like these for a long way, with one post office box having a piece of paper with the number of the next post office box written on it. This gets screwy after the third or fourth box.

Anyway, the post office is the simplified notion of RAM your OS gives application programs, a given post office box is a RAM location (byte or word), and a post office box number is a pointer.

The rest of the article is basically "You can program carefully enough to make C programs robust." and that is, in fact, true. I use robust C programs every day, one of them being the Linux kernel. However, the actual debate is over whether it's worth taking the time to be that careful when you could use a different language which makes a lot of mistakes impossible.

mstroeck• 15 years ago

This. I've always wondered what's so difficult about pointers for some people, mainly because I used a similar mental model from the very beginning.

Laurence Tratt: How can C Programs be so Reliable?

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