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    <p>Last year, I offered a bounty for information on configuration languages other than XML that provide schema validation for the contents of a configuration file. There were frustratingly few responses, as you can see if you follow this <a href="https://stackoverflow.com/questions/6079692/validating-files-having-tree-based-structures/">link</a>.</p> <p>Therefore, if you want schema validation, then I agree with nfechner that you should look at some schema languages for XML. You can find links to some of the more famous ones in <a href="http://en.wikipedia.org/wiki/XML_schema" rel="nofollow noreferrer">one</a> or <a href="http://en.wikipedia.org/wiki/XML_schema_language_comparison" rel="nofollow noreferrer">two</a> Wikipedia articles.</p> <p><em>If</em> you are not already committed to using XML, then you might want to check out <a href="http://www.config4star.org/" rel="nofollow noreferrer">Config4*</a> (of which I am the maintainer). I mention this because Config4* provides a schema validation language that is at least an order of magnitude easier to use than XML Schema. (The <em>only</em> other non-XML configuration language I discovered that has schema validation is YAML, but that functionality is available only via a Java or Ruby API, which is inconvenient for C/C++ applications.)</p> <p>Config4* provides a C++ API rather than a C API, but I suspect you will find it easy enough to put an <code>extern "C"</code> wrapper around a useful subset of the API.</p> <p>Regarding thread safety... <em>If</em> your applications will read a configuration file during single-threaded initialisation, and only afterwards allow multiple threads to query the configuration object, then I don't think any synchronisation will be required since the multiple threads will be invoking read-only operations. However, I suspect you already know that, and you are asking about thread safety because you expect to have some threads invoking query operations on a configuration object while other threads are concurrently invoking update operations on it. If you could give examples of some multi-threaded use cases you expect to have in your applications, then it might help people to offer advice that is relevant to your thread-safety requirements. As a fall-back technique, you could implement a synchronised delegation wrapper around the API of of whatever configuration library you use. For example (pseudo-code):</p> <pre><code>int config_lookup_int(const char * name) { int result; get_mutex_lock(); result = raw_api_lookup_int(name); release_mutex_lock(); return result; } </code></pre> <p>One last thing. Please elaborate on the <code>notify_config</code> functionality you are seeking.</p>
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    1. POApplication configuration : need your views
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    1. USCiaran McHale
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