title: Will `std::vector` do anything I haven't asked it to
body: <p>In C++, if I initialize a <code>std::vector v(100);</code> and never try to <code>resize()</code> nor <code>reserve()</code> it, is the <code>capacity()</code> guaranteed to stay the same all the time? I want to make sure that no memory alloc/freeing/realloc/etc is going on for perforance reasons. (Yes, it would affect performance; my functions are called all the time, and they <em>must</em> returrn quickly).</p>
  
  <p>Resuming it all:</p>
  
  <pre><code>std::vector&lt;float&gt; v;
  // somehow, `v' is initialized to have 100 elements
  void f() { // this function must return _very_ quickly
      /* do some processing, without ever calling v.resize() or v.reserve(), but
         accesing v.size() and v[i] all the time */
      /* it is guaranteed that no system calls (such as memory management)
         will take place here? */
  } // no objects on the stack whose destroyers might try to `delete' anything.
  </code></pre>