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POHow efficient is std::string compared to null-terminated strings?
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  1. POHow efficient is std::string compared to null-terminated strings?
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    copied!<p>I've discovered that <code>std::string</code>s are very slow compared to old-fashioned null-terminated strings, so much slow that they significantly slow down my overall program by a factor of 2.</p> <p>I expected STL to be slower, I didn't realise it was going to be this much slower. </p> <p>I'm using Visual Studio 2008, release mode. It shows assignment of a string to be 100-1000 times slower than <code>char*</code> assignment (it's very difficult to test the run-time of a <code>char*</code> assignment). I know it's not a fair comparison, a pointer assignment versus string copy, but my program has lots of string assignments and I'm not sure I could use the "<em>const reference</em>" trick in all places. With a reference counting implementation my program would have been fine, but these implementations don't seem to exist anymore.</p> <p>My real question is: why don't people use reference counting implementations anymore, and does this mean we all need to be much more careful about avoiding common performance pitfalls of std::string?</p> <p>My full code is below. </p> <pre><code>#include &lt;string&gt; #include &lt;iostream&gt; #include &lt;time.h&gt; using std::cout; void stop() { } int main(int argc, char* argv[]) { #define LIMIT 100000000 clock_t start; std::string foo1 = "Hello there buddy"; std::string foo2 = "Hello there buddy, yeah you too"; std::string f; start = clock(); for (int i=0; i &lt; LIMIT; i++) { stop(); f = foo1; foo1 = foo2; foo2 = f; } double stl = double(clock() - start) / CLOCKS\_PER\_SEC; start = clock(); for (int i=0; i &lt; LIMIT; i++) { stop(); } double emptyLoop = double(clock() - start) / CLOCKS_PER_SEC; char* goo1 = "Hello there buddy"; char* goo2 = "Hello there buddy, yeah you too"; char *g; start = clock(); for (int i=0; i &lt; LIMIT; i++) { stop(); g = goo1; goo1 = goo2; goo2 = g; } double charLoop = double(clock() - start) / CLOCKS_PER_SEC; cout &lt;&lt; "Empty loop = " &lt;&lt; emptyLoop &lt;&lt; "\n"; cout &lt;&lt; "char* loop = " &lt;&lt; charLoop &lt;&lt; "\n"; cout &lt;&lt; "std::string = " &lt;&lt; stl &lt;&lt; "\n"; cout &lt;&lt; "slowdown = " &lt;&lt; (stl - emptyLoop) / (charLoop - emptyLoop) &lt;&lt; "\n"; std::string wait; std::cin &gt;&gt; wait; return 0; } </code></pre>
 

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