notes

printf

, <html>
, <head>
, <title>printf cheat sheet</title>
, 
, 
, 
, <h2>printf formatting with Perl and Java</h2>
, 
, <p>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 <code>printf</code> example to get things started:</p>
, 
, <pre>
, printf(DQthe %s jumped over the %s, %d timesDQ, DQcowDQ, DQmoonDQ, 2);
, </pre>
, 
, <p>And here are three different Java <code>printf</code> examples, using different string formatting methods that are available to you in the Java programming language:</p>
, 
, <pre>
, System.out.format(DQthe %s jumped over the %s, %d timesDQ, DQcowDQ, DQmoonDQ, 2);
, System.err.format(DQthe %s jumped over the %s, %d timesDQ, DQcowDQ, DQmoonDQ, 2);
, String result = String.format(DQthe %s jumped over the %s, %d timesDQ, DQcowDQ, DQmoonDQ, 2);
, </pre>
, 
, <p>As you can see in that last <code>String.format</code> 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.</p>
, 
, <p>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.</p>
, 
, <h2>A summary of printf format specifiers</h2>
, 
, <p>Here’s a quick summary of the available <code>printf</code> format specifiers:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<td>%c</td>
, 			<td>character</td>
, 		</tr>
, 		<tr>
, 			<td>%d</td>
, 			<td>decimal (integer) number (base 10)</td>
, 		</tr>
, 		<tr>
, 			<td>%e</td>
, 			<td>exponential floating-point number</td>
, 		</tr>
, 		<tr>
, 			<td>%f</td>
, 			<td>floating-point number</td>
, 		</tr>
, 		<tr>
, 			<td>%i</td>
, 			<td>integer (base 10)</td>
, 		</tr>
, 		<tr>
, 			<td>%o</td>
, 			<td>octal number (base 8)</td>
, 		</tr>
, 		<tr>
, 			<td>%s</td>
, 			<td>a string of characters</td>
, 		</tr>
, 		<tr>
, 			<td>%u</td>
, 			<td>unsigned decimal (integer) number</td>
, 		</tr>
, 		<tr>
, 			<td>%x</td>
, 			<td>number in hexadecimal (base 16)</td>
, 		</tr>
, 		<tr>
, 			<td>%%</td>
, 			<td>print a percent sign</td>
, 		</tr>
, 		<tr>
, 			<td>\%</td>
, 			<td>print a percent sign</td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <h2>Controlling integer width with printf</h2>
, 
, <p>The <code>%3d</code> specifier is used with integers, and means a minimum width of three spaces, which, by default, will be right-justified:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<td>printf(DQ%3dDQ, 0);</td>
, 			<td class=DQtext-right code-fontDQ>0</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%3dDQ, 123456789);</td>
, 			<td class=DQtext-right code-fontDQ>123456789</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%3dDQ, -10);</td>
, 			<td class=DQtext-right code-fontDQ>-10</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%3dDQ, -123456789);</td>
, 			<td class=DQtext-right code-fontDQ>-123456789</td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <h2>Left-justifying printf integer output</h2>
, 
, <p>To left-justify integer output with <code>printf</code>, just add a minus sign (<code>-</code>) after the <code>%</code> symbol, like this:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<td>printf(DQ%-3dDQ, 0);</td>
, 			<td class=DQtext-left code-fontDQ>0</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%-3dDQ, 123456789);</td>
, 			<td class=DQtext-left code-fontDQ>123456789</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%-3dDQ, -10);</td>
, 			<td class=DQtext-left code-fontDQ>-10</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%-3dDQ, -123456789);</td>
, 			<td class=DQtext-left code-fontDQ>-123456789</td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <h2>The printf integer zero-fill option</h2>
, 
, <p>To zero-fill your <code>printf</code> integer output, just add a zero (<code>0</code>) after the <code>%</code> symbol, like this:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<td>printf(DQ%03dDQ, 0);</td>
, 			<td class=DQtext-right code-fontDQ>000</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%03dDQ, 1);</td>
, 			<td class=DQtext-right code-fontDQ>001</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%03dDQ, 123456789);</td>
, 			<td class=DQtext-right code-fontDQ>123456789</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%03dDQ, -10);</td>
, 			<td class=DQtext-right code-fontDQ>-10</td>
, 		</tr>
, 		<tr>
, 			<td>printf(DQ%03dDQ, -123456789);</td>
, 			<td class=DQtext-right code-fontDQ>-123456789</td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <h2>printf integer formatting</h2>
, 
, <p>As a summary of <code>printf</code> 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.</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<th>Description</th>
, 			<th>Code</th>
, 			<th>Result</th>
, 		</tr>
, 		<tr>
, 			<td>At least five wide</td>
, 			<td>printf(DQ%5dDQ, 10);</td>
, 			<td class=DQtext-right code-fontDQ>   10</td>
, 		</tr>
, 		<tr>
, 			<td>At least five-wide, left-justified</td>
, 			<td>printf(DQ%-5dDQ, 10);</td>
, 			<td class=DQtext-right code-fontDQ>10   </td>
, 		</tr>
, 		<tr>
, 			<td>At least five-wide, zero-filled</td>
, 			<td>printf(DQ%05dDQ, 10);</td>
, 			<td class=DQtext-right code-fontDQ>00010</td>
, 		</tr>
, 		<tr>
, 			<td>At least five-wide, with a plus sign</td>
, 			<td>printf(DQ%+5dDQ, 10);</td>
, 			<td class=DQtext-right code-fontDQ>  +10</td>
, 		</tr>
, 		<tr>
, 			<td>Five-wide, plus sign, left-justified</td>
, 			<td>printf(DQ%-+5dDQ, 10);</td>
, 			<td class=DQtext-right code-fontDQ>+10  </td>
, 		</tr>
, 	</tbody>
, </table>
, 
,     
, 
, <h2>formatting floating point numbers with printf</h2>
, 
, <p>Here are several examples showing how to format floating-point numbers with <code>printf</code>:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<th>Description</th>
, 			<th>Code</th>
, 			<th>Result</th>
, 		</tr>
, 		<tr>
, 			<td>Print one position after the decimal</td>
, 			<td>printf(DQ%.1fDQ, 10.3456);</td>
, 			<td class=DQtext-right code-fontDQ>10.3</td>
, 		</tr>
, 		<tr>
, 			<td>Two positions after the decimal</td>
, 			<td>printf(DQ%.2fDQ, 10.3456);</td>
, 			<td class=DQtext-right code-fontDQ>10.35</td>
, 		</tr>
, 		<tr>
, 			<td>Eight-wide, two positions after the decimal</td>
, 			<td>printf(DQ%8.2fDQ, 10.3456);</td>
, 			<td class=DQtext-right code-fontDQ>   10.35</td>
, 		</tr>
, 		<tr>
, 			<td>Eight-wide, four positions after the decimal</td>
, 			<td>printf(DQ%8.4fDQ, 10.3456);</td>
, 			<td class=DQtext-right code-fontDQ> 10.3456</td>
, 		</tr>
, 		<tr>
, 			<td>Eight-wide, two positions after the decimal, zero-filled</td>
, 			<td>printf(DQ%08.2fDQ, 10.3456);</td>
, 			<td class=DQtext-right code-fontDQ>00010.35</td>
, 		</tr>
, 		<tr>
, 			<td>Eight-wide, two positions after the decimal, left-justified</td>
, 			<td>printf(DQ%-8.2fDQ, 10.3456);</td>
, 			<td class=DQtext-right code-fontDQ>10.35   </td>
, 		</tr>
, 		<tr>
, 			<td>Printing a much larger number with that same format</td>
, 			<td>printf(DQ%-8.2fDQ, 101234567.3456);</td>
, 			<td class=DQtext-right code-fontDQ>101234567.35</td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <h2>printf string formatting</h2>
, 
, <p>Here are several examples that show how to format string output with <code>printf</code>:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<th>Description</th>
, 			<th>Code</th>
, 			<th>Result</th>
, 		</tr>
, 		<tr>
, 			<td>A simple string</td>
, 			<td>printf(DQ%sDQ, DQHelloDQ);</td>
, 			<td class=DQtext-right code-fontDQ>Hello</td>
, 		</tr>
, 		<tr>
, 			<td>A string with a minimum length</td>
, 			<td>printf(DQ%10sDQ, DQHelloDQ);</td>
, 			<td class=DQtext-right code-fontDQ>     Hello</td>
, 		</tr>
, 		<tr>
, 			<td>Minimum length, left-justified</td>
, 			<td>printf(DQ%-10sDQ, DQHelloDQ);</td>
, 			<td class=DQtext-right code-fontDQ>Hello     </td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <h2>printf special characters</h2>
, 
, <p>The following character sequences have a special meaning when used as <code>printf</code> format specifiers:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<td>\a</td>
, 			<td>audible alert</td>
, 		</tr>
, 		<tr>
, 			<td>\b</td>
, 			<td>backspace</td>
, 		</tr>
, 		<tr>
, 			<td>\f</td>
, 			<td>form feed</td>
, 		</tr>
, 		<tr>
, 			<td>\n</td>
, 			<td>newline, or linefeed</td>
, 		</tr>
, 		<tr>
, 			<td>\r</td>
, 			<td>carriage return</td>
, 		</tr>
, 		<tr>
, 			<td>\t</td>
, 			<td>tab</td>
, 		</tr>
, 		<tr>
, 			<td>\v</td>
, 			<td>vertical tab</td>
, 		</tr>
, 		<tr>
, 			<td>\\</td>
, 			<td>backslash</td>
, 		</tr>
, 	</tbody>
, </table>
, 
, <p>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.</p>
, 
, <p>Here are a few examples of how to use these special characters:</p>
, 
, <table>
, 	<tbody>
, 		<tr>
, 			<th>Description</th>
, 			<th>Code</th>
, 			<th>Result</th>
, 		</tr>
, 		<tr>
, 			<td>Insert a tab character in a string</td>
, 			<td>printf(DQHello\tworldDQ);</td>
, 			<td class=DQtext-left code-fontDQ>Hello world</td>
, 		</tr>
, 		<tr>
, 			<td>Insert a newline character in a string</td>
, 			<td>printf(DQHello\nworldDQ);</td>
, 			<td class=DQtext-left code-fontDQ>Hello<br />
, 			world</td>
, 		</tr>
, 		<tr>
, 			<td>Typical use of the newline character</td>
, 			<td>printf(DQHello world\nDQ);</td>
, 			<td class=DQtext-left code-fontDQ>Hello world</td>
, 		</tr>
, 		<tr>
, 			<td>A DOS/Windows path with backslash characters</td>
, 			<td>printf(DQC:\\Windows\\System32\\DQ);</td>
, 			<td class=DQtext-left code-fontDQ>C:\Windows\System32\</td>
, 		</tr>
, 	</tbody>
, </table>
,     
, 
, </body>
, </html>