A `printf` format reference page (cheat sheet) (C, Java, Scala, etc.)

Summary: This page is a printf formatting cheat sheet or reference page. I originally created this printf cheat sheet for my own programming purposes, and then thought it might be helpful to share it here.

Many languages, same syntax

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, Python, Perl, PHP, Ruby, Scala, and others. This means that your printf knowledge is reusable, which is a good thing.

printf formatting with Java and Perl

In this cheat sheet I’ll show all the examples using Perl, but at first it might help to see one example using both Perl and Java. Therefore, here’s a simple Perl printf example to get things started:

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

And here are three different Java printf examples, using different string formatting methods that are available to you in the Java programming language:

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’ll use Perl examples, but again, the actual format specifier strings can be used in many different languages.

A summary of printf format specifiers

Here’s a quick summary of the available printf format specifiers:

%c character
%d decimal (integer) number (base 10)
%e exponential floating-point number
%f floating-point number
%i integer (base 10)
%o octal number (base 8)
%s a string of characters
%u unsigned decimal (integer) number
%x number in hexadecimal (base 16)
%% print a percent sign
\% print a percent sign

Controlling integer width with printf

The %3d specifier is used with integers, and means a minimum width of three spaces, which, by default, will be right-justified:

printf("%3d", 0); 0
printf("%3d", 123456789); 123456789
printf("%3d", -10); -10
printf("%3d", -123456789); -123456789

Left-justifying printf integer output

To left-justify integer output with printf, just add a minus sign (-) after the % symbol, like this:

printf("%-3d", 0); 0
printf("%-3d", 123456789); 123456789
printf("%-3d", -10); -10
printf("%-3d", -123456789); -123456789

The printf integer zero-fill option

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

printf("%03d", 0); 000
printf("%03d", 1); 001
printf("%03d", 123456789); 123456789
printf("%03d", -10); -10
printf("%03d", -123456789); -123456789

printf integer formatting

As a summary of printf integer formatting, here’s a little collection of integer formatting examples. Several different options are shown, including a minimum width specification, left-justified, zero-filled, and also a plus sign for positive numbers.

Description Code Result
At least five wide printf("'%5d'", 10); '   10'
At least five-wide, left-justified printf("'%-5d'", 10); '10   '
At least five-wide, zero-filled printf("'%05d'", 10); '00010'
At least five-wide, with a plus sign printf("'%+5d'", 10); '  +10'
Five-wide, plus sign, left-justified printf("'%-+5d'", 10); '+10  '

formatting floating point numbers with printf

Here are several examples showing how to format floating-point numbers with printf:

Description Code Result
Print one position after the decimal printf("'%.1f'", 10.3456); '10.3'
Two positions after the decimal printf("'%.2f'", 10.3456); '10.35'
Eight-wide, two positions after the decimal printf("'%8.2f'", 10.3456); '   10.35'
Eight-wide, four positions after the decimal printf("'%8.4f'", 10.3456); ' 10.3456'
Eight-wide, two positions after the decimal, zero-filled printf("'%08.2f'", 10.3456); '00010.35'
Eight-wide, two positions after the decimal, left-justified printf("'%-8.2f'", 10.3456); '10.35   '
Printing a much larger number with that same format printf("'%-8.2f'", 101234567.3456); '101234567.35'

printf string formatting

Here are several examples that show how to format string output with printf:

Description Code Result
A simple string printf("'%s'", "Hello"); 'Hello'
A string with a minimum length printf("'%10s'", "Hello"); '     Hello'
Minimum length, left-justified printf("'%-10s'", "Hello"); 'Hello     '

printf special characters

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

\a audible alert
\b backspace
\f form feed
\n newline, or linefeed
\r carriage return
\t tab
\v vertical tab
\\ backslash

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 these special characters:

Description Code Result
Insert a tab character in a string printf("Hello\tworld"); Hello world
Insert a newline character in a string printf("Hello\nworld"); Hello
Typical use of the newline character printf("Hello world\n"); Hello world
A DOS/Windows path with backslash characters printf("C:\\Windows\\System32\\"); C:\Windows\System32\

Related printf content

Here are a few links to other “printf” tutorials on my website:

And here’s a link to the Java formatter javadoc.