I've created a printf format specifier cheat sheet, and thought I would share it here. A cool thing about the printf formatting syntax is that the specifiers you can use are very similar, if not identical, between several different languages, including C, C++, Java, Perl, and Ruby, so your knowledge is reusable, which I like.

A quick look at Perl and Java

In this cheat sheet I'm going to show all the examples using Perl, but I thought at first it might help to one example using both Perl and Java. So, here's a simple source code example using Perl:

printf("the %s jumped over the %s, %d times", "cow", "moon", 2);

And here are three different ways of using printf format specifier syntax with Java:

System.out.format("the %s jumped over the %s, %d times", "cow", "moon", 2);
System.err.format("the %s jumped over the %s, %d times", "cow", "moon", 2);
String result = String.format("the %s jumped over the %s, %d times", "cow", "moon", 2);

As you can see in that last String.format example, that line of code doesn't print any output, while the first line prints to standard output, and the second line prints to standard error.

In the remainder of this document I'm going to use Perl examples, but again, the actual format specifier strings can be used in many different languages.

A summary of the printf format specifiers

Here's a quick summary of the available print format specifiers:

Controlling the width of integer output

The "%3d" specifier means a minimum width of three spaces, which, by default, will be right-justified. (Note: the alignment is not currently being displayed properly here.)

Left-justify integer output

To left-justify those previous, just add a minus sign (-) after the % symbol, like this:

The zero-fill option

To zero-fill your integer output, just add a zero (0) after the % symbol, like this:

Printing integers with formatting

Here is a collection of examples for integer printing. Several different options are shown, including a minimum width specification, left-justified, zero-filled, and also a plus sign for positive numbers.

Printing floating point numbers

Here are several examples showing how to print floating-point numbers.

How to print strings with printf formatting

Here are several printf formatting examples that show how to format string output with printf format specifiers.

Summary of special printf characters

The following character sequences have a special meaning when used as printf format specifiers:

As you can see from that last example, because the backslash character itself is treated specially, you have to print two backslash characters in a row to get one backslash character to appear in your output.

Here are a few examples of how to use this special characters: