title: Why is the predefined macro __STDC_VERSION__ undefined?
body: <p>I want to know which C standard I am currently using in my Visual Studio C++, but I have a trouble using the <code>__STDC_VERSION__</code> predefined macro and other C99 predefined macros - an error indicating that this identifier is not defined appears and when I used <code>#ifndef __STDC_VERSION__</code> it seems that it is not defined. Does this mean that I am using ANSI C?</p>
  
  <p>Below is a sample code for using <code>__STDC_VERSION__</code>:</p>
  
  <pre><code>int main(void) {
     printf("%d\n", __STDC_VERSION__);
     return 0;
  }
  </code></pre>