printf quick start quide

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.

printf formatting with Java versus C

In this cheat sheet, all examples are shown using C/C++, which differs from Java by not requiring the System.out. part of the command. 
// In Java language
System.out.printf("The child jumped up and down %d times.",  3 );

// In C language
printf("The child jumped up and down %d times.",  3 );
The remainder of this page uses C examples for brevity. Note that the actual format specifier strings can be used in many different languages exactly as shown.

A summary of printf format specifiers

Here’s a quick summary of the most commonly used printf format specifiers:

%c single character
%d decimal number
  ie, integer a base 10 whole number   like 3
%f floating-point number
  ie, has a decimal point   like 3.096
%s a string of characters

Controlling integer width

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

Several different options allow you to include a minimum width specification, left-justify, or include 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, with a plus sign printf("'%+5d'", 10); '  +10'
Five-wide, plus sign, left-justified printf("'%-+5d'", 10); '+10  '

formatting floating point numbers

Examples:

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, 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

Examples:

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:

\n newline
\t tab
\\ backslash
%% percent

As you can see from that last two examples, because the backslash character and the percent character themselves are treated specially, you have to print two backslash characters in a row to get one backslash character to appear or two percent characters in a row to get a single persent 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
world
Typical use of the newline character printf("Hello world\n"); Hello world
backslash characters printf("C:\\Windows\\System32\\"); C:\Windows\System32\
percent characters printf("The exam score is 97%%"); 97%