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| <h4 class="subsection">12.12.1 Formatted Output Basics</h4> |
| |
| <p>The <code>printf</code> function can be used to print any number of arguments. |
| The template string argument you supply in a call provides |
| information not only about the number of additional arguments, but also |
| about their types and what style should be used for printing them. |
| |
| <p>Ordinary characters in the template string are simply written to the |
| output stream as-is, while <dfn>conversion specifications</dfn> introduced by |
| a ‘<samp><span class="samp">%</span></samp>’ character in the template cause subsequent arguments to be |
| formatted and written to the output stream. For example, |
| <a name="index-conversion-specifications-_0028_0040code_007bprintf_007d_0029-1019"></a> |
| <pre class="smallexample"> int pct = 37; |
| char filename[] = "foo.txt"; |
| printf ("Processing of `%s' is %d%% finished.\nPlease be patient.\n", |
| filename, pct); |
| </pre> |
| <p class="noindent">produces output like |
| |
| <pre class="smallexample"> Processing of `foo.txt' is 37% finished. |
| Please be patient. |
| </pre> |
| <p>This example shows the use of the ‘<samp><span class="samp">%d</span></samp>’ conversion to specify that |
| an <code>int</code> argument should be printed in decimal notation, the |
| ‘<samp><span class="samp">%s</span></samp>’ conversion to specify printing of a string argument, and |
| the ‘<samp><span class="samp">%%</span></samp>’ conversion to print a literal ‘<samp><span class="samp">%</span></samp>’ character. |
| |
| <p>There are also conversions for printing an integer argument as an |
| unsigned value in octal, decimal, or hexadecimal radix (‘<samp><span class="samp">%o</span></samp>’, |
| ‘<samp><span class="samp">%u</span></samp>’, or ‘<samp><span class="samp">%x</span></samp>’, respectively); or as a character value |
| (‘<samp><span class="samp">%c</span></samp>’). |
| |
| <p>Floating-point numbers can be printed in normal, fixed-point notation |
| using the ‘<samp><span class="samp">%f</span></samp>’ conversion or in exponential notation using the |
| ‘<samp><span class="samp">%e</span></samp>’ conversion. The ‘<samp><span class="samp">%g</span></samp>’ conversion uses either ‘<samp><span class="samp">%e</span></samp>’ |
| or ‘<samp><span class="samp">%f</span></samp>’ format, depending on what is more appropriate for the |
| magnitude of the particular number. |
| |
| <p>You can control formatting more precisely by writing <dfn>modifiers</dfn> |
| between the ‘<samp><span class="samp">%</span></samp>’ and the character that indicates which conversion |
| to apply. These slightly alter the ordinary behavior of the conversion. |
| For example, most conversion specifications permit you to specify a |
| minimum field width and a flag indicating whether you want the result |
| left- or right-justified within the field. |
| |
| <p>The specific flags and modifiers that are permitted and their |
| interpretation vary depending on the particular conversion. They're all |
| described in more detail in the following sections. Don't worry if this |
| all seems excessively complicated at first; you can almost always get |
| reasonable free-format output without using any of the modifiers at all. |
| The modifiers are mostly used to make the output look “prettier” in |
| tables. |
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