Author:

• Name: Brian Westley
  Location: US - United States of America (United States)

To build:

    make all

There is another version which is the original entry. See Alternate code for details as to how to use and why it was made the alt version.

To use:

    ./clock1.sh
    ./clock2.sh
    ./clock3.sh

Try:

    ./try.sh

Alternate code:

The original version had a display problem in modern systems which somewhat affected the usability of the program. This alternate code, the original, is provided, to show the differences.

Alternate build:

    make alt

Alternate try:

    ./try.alt.sh

Judges’ remarks:

Time and time again, Brian Westley seems to come up with a winning entry! 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 remarks:

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.sh, clock2.sh, and clock3.sh.

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(3) 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 but makes the code larger.

The code is simple; the arguments passed are:

    ./westley 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(3) 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.

Primary files

• westley.c - entry source code
• Makefile - entry Makefile
• westley.alt.c - alternate source code
• westley.orig.c - original source code
• clock1.sh - script to try first clock
• clock2.sh - script to try second clock
• clock3.sh - script to try third clock
• try.alt.sh - script to try alternate code
• try.sh - script to try entry

Secondary files

• 1996_westley.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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