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POC++ format macro / inline ostringstream
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  1. POC++ format macro / inline ostringstream
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    copied!<p>I'm trying to write a macro that would allow me to do something like: <code>FORMAT(a &lt;&lt; "b" &lt;&lt; c &lt;&lt; d)</code>, and the result would be a string -- the same as creating an ostringstream, inserting <code>a...d</code>, and returning <code>.str()</code>. Something like:</p> <pre><code>string f(){ ostringstream o; o &lt;&lt; a &lt;&lt; "b" &lt;&lt; c &lt;&lt; d; return o.str() } </code></pre> <p>Essentially, <code>FORMAT(a &lt;&lt; "b" &lt;&lt; c &lt;&lt; d) == f()</code>.</p> <p>First, I tried:</p> <pre><code>1: #define FORMAT(items) \ ((std::ostringstream&amp;)(std::ostringstream() &lt;&lt; items)).str() </code></pre> <p>If the very first item is a C string (<code>const char *</code>), it will print the address of the string in hex, and the next items will print fine. If the very first item is an <code>std::string</code>, it will fail to compile (no matching operator <code>&lt;&lt;</code>).</p> <p>This:</p> <pre><code>2: #define FORMAT(items) \ ((std::ostringstream&amp;)(std::ostringstream() &lt;&lt; 0 &lt;&lt; '\b' &lt;&lt; items)).str() </code></pre> <p>gives what seems like the right output, but the <code>0</code> and <code>\b</code> are present in the string of course.</p> <p>The following seems to work, but compiles with warnings (taking address of temporary):</p> <pre><code>3: #define FORMAT(items) \ ((std::ostringstream&amp;)(*((std::ostream*)(&amp;std::ostringstream())) &lt;&lt; items)).str() </code></pre> <p>Does anyone know why 1 prints the address of the c-string and fails to compile with the <code>std::string</code>? Aren't 1 and 3 essentially the same?</p> <p>I suspect that C++0x variadic templates will make <code>format(a, "b", c, d)</code> possible. But is there a way to solve this now?</p>
 

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