A `printf` format reference page (cheat sheet)

Summary: This page is a printf formatting cheat sheet. I originally created this cheat sheet for my own purposes, and then thought I would share it here.

A great thing about the printf formatting syntax is that the format specifiers you can use are very similar — if not identical — between different languages, including C, C++, Java, Perl, PHP, Ruby, Scala, and others. This means that your printf knowledge is reusable, which is a good thing.

A Flutter function to convert a TimeOfDay to a String (formatted)

If you ever need a Dart/Flutter method to format a TimeOfDay variable — i.e., convert a TimeOfDay to a String — I can confirm that this method works:

String formatTimeOfDay(TimeOfDay tod) {
    final now = new;
    final dt = DateTime(now.year, now.month,, tod.hour, tod.minute);
    final format =;  //"6:00 AM"
    return format.format(dt);

An example of Scala’s `f` string interpolator

With Scala it’s common to embed variables in strings like this with the s string interpolator:

val name = "Fred"
println(s"My name is $name.")

That’s cool, but when you need to format your string, Scala gives you an even more powerful tool: the f string interpolator. Here’s an example of how I just did this in my LittleLogger logging library:

How to convert Asciidoc to HTML

As a brief note to self, if you need to convert an Asciidoc file named test1.adoc to HTML format, this command works:

asciidoc -o test1.html test1.adoc

Of course a key here is that you need the asciidoc command installed. I installed it on my Mac with Homebrew, something like brew install asciidoc. I don’t like the HTML that this approach generates, so I’ll keep looking for something better.

Scala String.format error: overloaded method value format with alternatives alvin November 10, 2018 - 3:33pm

I was writing some Scala code like this today:

val sb = new StringBuilder
for (b: Byte <- mdOut.digest) {
    val hexString: String = String.format("%02x", b)

and encountered this error message:

Some Scala Long, Date, and SimpleDateFormat examples

At some point I’ll get all of my Scala “date utilities” together in a single class (object, actually), but until then, here are a couple of date utility methods I wrote for my Scrupal6 project (a replacement for Drupal 6):

Format of the Linux crontab date and time fields

I’ve written several things about the Linux cron command and crontab file format before, and as a quick note, here’s some information on the format of the crontab date and time fields.

Crontab date/time fields

First, from the crontab man page documentation:

Scala number, date, and formatting examples

This short blog post contains a collection of Scala number and date examples. I created most of these in the process of writing the Scala Cookbook. Unlike the Cookbook, I don’t describe the examples here much at all, I just show the examples, mostly as a reference for myself (and anyone else that can benefit from them).

Scala numeric types

Scala has these numeric types:

Scaladoc syntax examples (Scaladoc tags, wiki markup)

Table of Contents1 - An example of Scaladoc tags and wiki formatting2 - Sample Scaladoc output3 - Common tags4 - Scaladoc “wiki” character formatting tags5 - Scaladoc “wiki” paragraph formatting tags6 - Generating Scaladoc documentation with SBT7 - See Also8 - The Scala Cookbook

In this article I share some examples of Scala’s Scaladoc syntax, including common Scaladoc tags, and the wiki-style of markup that Scaladoc supports.


(this space left open to make room for the table of contents over there -->)


Back to top

An example of Scaladoc tags and wiki formatting

You can mark up your source code using Scaladoc tags as well as a wiki-like syntax. The following code shows many of the Scaladoc tags and a few of the wiki-style markup tags: