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    <p>The direct answer is that yes, that's okay.</p> <p>A lot of people have thrown around various ideas of how to improve speed, but there seems to be quite a bit of disagreement over which is most effective. I decided to write a quick test program to get at least some idea of which techniques did what.</p> <pre><code>#include &lt;iostream&gt; #include &lt;string&gt; #include &lt;sstream&gt; #include &lt;time.h&gt; #include &lt;iomanip&gt; #include &lt;algorithm&gt; #include &lt;iterator&gt; #include &lt;stdio.h&gt; char fmt[] = "%s\n"; static const int count = 3000000; static char const *const string = "This is a string."; static std::string s = std::string(string) + "\n"; void show_time(void (*f)(), char const *caption) { clock_t start = clock(); f(); clock_t ticks = clock()-start; std::cerr &lt;&lt; std::setw(30) &lt;&lt; caption &lt;&lt; ": " &lt;&lt; (double)ticks/CLOCKS_PER_SEC &lt;&lt; "\n"; } void use_printf() { for (int i=0; i&lt;count; i++) printf(fmt, string); } void use_puts() { for (int i=0; i&lt;count; i++) puts(string); } void use_cout() { for (int i=0; i&lt;count; i++) std::cout &lt;&lt; string &lt;&lt; "\n"; } void use_cout_unsync() { std::cout.sync_with_stdio(false); for (int i=0; i&lt;count; i++) std::cout &lt;&lt; string &lt;&lt; "\n"; std::cout.sync_with_stdio(true); } void use_stringstream() { std::stringstream temp; for (int i=0; i&lt;count; i++) temp &lt;&lt; string &lt;&lt; "\n"; std::cout &lt;&lt; temp.str(); } void use_endl() { for (int i=0; i&lt;count; i++) std::cout &lt;&lt; string &lt;&lt; std::endl; } void use_fill_n() { std::fill_n(std::ostream_iterator&lt;char const *&gt;(std::cout, "\n"), count, string); } void use_write() { for (int i = 0; i &lt; count; i++) std::cout.write(s.data(), s.size()); } int main() { show_time(use_printf, "Time using printf"); show_time(use_puts, "Time using puts"); show_time(use_cout, "Time using cout (synced)"); show_time(use_cout_unsync, "Time using cout (un-synced)"); show_time(use_stringstream, "Time using stringstream"); show_time(use_endl, "Time using endl"); show_time(use_fill_n, "Time using fill_n"); show_time(use_write, "Time using write"); return 0; } </code></pre> <p>I ran this on Windows after compiling with VC++ 2013 (both x86 and x64 versions). Output from one run (with output redirected to a disk file) looked like this:</p> <pre class="lang-none prettyprint-override"><code> Time using printf: 0.953 Time using puts: 0.567 Time using cout (synced): 0.736 Time using cout (un-synced): 0.714 Time using stringstream: 0.725 Time using endl: 20.097 Time using fill_n: 0.749 Time using write: 0.499 </code></pre> <p>As expected, results vary, but there are a few points I found interesting:</p> <ol><li>printf/puts are much faster than cout when writing to the NUL device</li> <ul><li>but cout keeps up quite nicely when writing to a real file</li></ul> <li>Quite a few proposed optimizations accomplish little <ul><li>In my testing, fill_n is about as fast as anything else</li></ul></li> <li>By far the biggest optimization is avoiding endl</li> <li>cout.write gave the fastest time (though probably not by a significant margin</li></ol> <p>I've recently edited the code to force a call to <code>printf</code>. Anders Kaseorg was kind enough to point out--that <code>g++</code> recognizes the specific sequence <code>printf("%s\n", foo);</code> is equivalent to <code>puts(foo);</code>, and generates code accordingly (i.e., generates code to call <code>puts</code> instead of <code>printf</code>). Moving the format string to a global array, and passing that as the format string produces identical output, but forces it to be produced via <code>printf</code> instead of <code>puts</code>. Of course, it's possible they might optimize around this some day as well, but at least for now (g++ 5.1) a test with <code>g++ -O3 -S</code> confirms that it's actually calling <code>printf</code> (where the previous code compiled to a call to <code>puts</code>).</p>
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    1. COThank you for the thorough test. I always thought that `endl` was simply an alias to `"\n"`. As I can see, `endl` calls a flush too, while using `"\n"` will do buffering, just like printf.
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    2. CO@Jerry Coffin: excellent answer! I never realized that avoiding `std::endl` could give such a speed-jump.
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    3. COExcellent answer, but on VCpp Express 2010 it's needed to include <iterator> as well otherwise this error will be shown: "error C2039: 'ostream_iterator' : is not a member of 'std'"
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