title: C size_t not printing in printf
body: <p>I have two strings, both of which are equal, and I get their lengths like this </p>
  
  <pre><code>size_t len = strlen(s1);
  size_t len2 = strlen(s2);
  </code></pre>
  
  <p>I need to know what those are equal to, since the strings will not always be equal, so I tried printing out both values like this </p>
  
  <pre><code>printf("len1: %zu len2: %zu", len, len2);
  </code></pre>
  
  <p>but, this prints nothing. If I put this</p>
  
  <pre><code>printf("%s %s\n", s1, s2);
  </code></pre>
  
  <p>in the line above it, it prints out <code>test string test string</code>, which tells me that neither string is <code>NULL</code>. What is causing the string lengths to not print?</p>