title: c++ integer type automatic 64 bit
body: <p>I am using <code>size_t</code> for unsigned integer in my code. It has an advantage, if my computer support 64 bit, <code>size_t</code> will be <code>unsigned long long int</code>, otherwise, it is <code>unsigned int</code>. My code can run on both 32 bit and 64 bit platform.</p>
  
  <p>Is there a similar signed integer? If the platform only support 32 bit, it is <code>int</code>, if the platform support 64 bit, it is <code>long long int</code>. </p>
  
  <p>I can achieve this by setting a flag:</p>
  
  <pre><code>#ifdef USE_INT64
      #define MY_INT int
  #else
      #define MY_INT long long int
  #endif
  </code></pre>
  
  <p>Then use <code>MY_INT</code>. However I need to define <code>USE_INT64</code> and include this header for all my code. If there is something similar to <code>size_t</code>, it will be great. </p>