ioccc/1996/westley/README.md

Best One Liner:

Brian Westley (Merlyn LeRoy on Usenet)
1906 James Ave.
St. Paul, MN  55105
USA

http://www.visi.com/~westley/index.html

To build:

    make all

To run

sh ./clock1

Judges' comments

Also try:

sh ./clock2

And for a good time, try:

sh ./clock3

Time and time again, Brian Westley seems to come up with a winner! We are amazed at how much is being done with only one relatively short line. We think you will as well if you take the time to understand it.

Author's comments

This 1-line program allows various analog ASCII clocks to print out the time; the ASCII clock is built from the command line arguments, so many different types of clocks can be generated. Three different scripts are supplied to print out a grandfather clock, a mantle clock that runs backwards, and a linear-style clock. (they are clock1, clock2, and clock3)

The program makes the following (possibly non-portable) assumptions:

1. Command line strings can be written to

2. argv[0] can be written to as if it were a long *

3. The first three elements of the struct * returned by localtime() are seconds, minutes, hours, and all are ints

4. My sample scripts assume ASCII, though this is not inherent in the code, just my sample scripts

These assumptions are pretty reasonable. 2) can be eliminated by makes the code larger.

The code is simple; the arguments passed are:

    prog minute_map hour_map hand_symbol clock_image

The program merely takes the minute (0-59) and the hour (0-23) values, looks up the offsets in minute_map and hour_map and writes the hand_symbol for each into the clock_image string. This string is then printed.

The for() loop starts by calling time() with argv[0], so the time value (a long) is written into the program name. The for() control value is argc, which starts at 5, but the /=2 statement is executed before the test, so the for() loop is executed twice, with h=2, then h=1 (for hour & minute).

The statement of the for() loop takes the hour or minute field of the struct returned by localtime() by casting it to an int* and dereferencing element [h]. It is slightly smaller to use the trick h[(int*)localtime(*m)] instead of ((int*)localtime(*m))[h].

This value is in turn indexed into the hour_map or minute_map parameter to determine where the 'hand' symbol should be written into the clock_image.

Note that the hands move in a quantum fashion; 3:59 looks deceptively like 2:59, since the hour hand will be at the 3 position. It won't move until both hands click over at 4:00.