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copied!<p>So, I took a look at <a href="http://www.boost.org/doc/libs/1_41_0/index.html" rel="nofollow noreferrer">Boost.IOstreams</a> and here's what I've come up with:</p> <pre><code>class TestSink : public boost::iostreams::sink { public: std::streamsize write( const char * s, std::streamsize n ) { std::string message( s, n ); /* This would add a message to the log instead of cout. The log implementation is threadsafe. */ std::cout << message << std::endl; return n; } }; </code></pre> <p><code>TestSink</code> can be used to create a stream-buffer (see <a href="http://www.boost.org/doc/libs/1_41_0/libs/iostreams/doc/guide/generic_streams.html#stream_buffer" rel="nofollow noreferrer">stream_buffer-template</a>). Every thread will receive it's own instance of <code>TestSink</code>, but all <code>TestSinks</code> will write to the same log. <code>TestSink</code> is used as follows:</p> <pre><code>TestSink sink; boost::iostreams::stream_buffer< TestSink > testbuf( sink, 50000 ); std::ostream out( &testbuf ); for ( int i = 0; i < 10000; i++ ) out << "test" << i; out << std::endl; </code></pre> <p>The important fact here is, that <code>TestSink.write</code> is only called when the stream is flushed (<code>std::endl</code> or <code>std::flush</code>), or when the internal buffer of the <code>stream_buffer</code> instance is full (the default buffer size cannot hold 40000 chars, so I initalize it to 50000). In this program, <code>TestSink.write</code> is called exactly once (the output is too long to post here). This way I can write logmessage using normal formatted stream-IO without any temporary variables and be sure, that the message is posted to the log in one piece when I flush the stream.</p> <p>I will leave the question open another day, in case there are different suggestions/problems I have not considered.</p>

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