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| <h3 class="section">12.13 Customizing <code>printf</code></h3> |
| |
| <p><a name="index-customizing-_0040code_007bprintf_007d-1061"></a><a name="index-defining-new-_0040code_007bprintf_007d-conversions-1062"></a><a name="index-extending-_0040code_007bprintf_007d-1063"></a> |
| The GNU C library lets you define your own custom conversion specifiers |
| for <code>printf</code> template strings, to teach <code>printf</code> clever ways |
| to print the important data structures of your program. |
| |
| <p>The way you do this is by registering the conversion with the function |
| <code>register_printf_function</code>; see <a href="Registering-New-Conversions.html#Registering-New-Conversions">Registering New Conversions</a>. |
| One of the arguments you pass to this function is a pointer to a handler |
| function that produces the actual output; see <a href="Defining-the-Output-Handler.html#Defining-the-Output-Handler">Defining the Output Handler</a>, for information on how to write this function. |
| |
| <p>You can also install a function that just returns information about the |
| number and type of arguments expected by the conversion specifier. |
| See <a href="Parsing-a-Template-String.html#Parsing-a-Template-String">Parsing a Template String</a>, for information about this. |
| |
| <p>The facilities of this section are declared in the header file |
| <samp><span class="file">printf.h</span></samp>. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Registering-New-Conversions.html#Registering-New-Conversions">Registering New Conversions</a>: Using <code>register_printf_function</code> |
| to register a new output conversion. |
| <li><a accesskey="2" href="Conversion-Specifier-Options.html#Conversion-Specifier-Options">Conversion Specifier Options</a>: The handler must be able to get |
| the options specified in the |
| template when it is called. |
| <li><a accesskey="3" href="Defining-the-Output-Handler.html#Defining-the-Output-Handler">Defining the Output Handler</a>: Defining the handler and arginfo |
| functions that are passed as arguments |
| to <code>register_printf_function</code>. |
| <li><a accesskey="4" href="Printf-Extension-Example.html#Printf-Extension-Example">Printf Extension Example</a>: How to define a <code>printf</code> |
| handler function. |
| <li><a accesskey="5" href="Predefined-Printf-Handlers.html#Predefined-Printf-Handlers">Predefined Printf Handlers</a>: Predefined <code>printf</code> handlers. |
| </ul> |
| |
| <p><strong>Portability Note:</strong> The ability to extend the syntax of |
| <code>printf</code> template strings is a GNU extension. ISO standard C has |
| nothing similar. |
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