title: lldb: Couldn't materialize: couldn't get the value of variable
body: <p>I have compiled a cpp file with this command line: <code>g++ -g test.cpp</code></p>
  
  <p>It throws an exception at line 28. I want to investigate the cause by inspecting the variables in lldb. I set a break point at line 28 and run the <code>a.out</code> in lldb.  </p>
  
  <pre><code>(lldb) n
  Process 84233 stopped
  * thread #1: tid = 0xa44b86, 0x00000001000017fb a.out`say(s=&lt;unavailable&gt;) + 987 at so.cpp:28, queue = 'com.apple.main-thread', stop reason = step over
      frame #0: 0x00000001000017fb a.out`say(s=&lt;unavailable&gt;) + 987 at so.cpp:28
     25       }
     26       else{
     27           s.insert(0, to_string(sz));
  -&gt; 28           s.erase(2, sz-1);
     29       }
     30       return s;
     31   }
  (lldb) po s
  error: Couldn't materialize: couldn't get the value of variable s: variable not available
  Errored out in Execute, couldn't PrepareToExecuteJITExpression
  </code></pre>
  
  <p>Why the error message? How can I inspect the variable <code>s</code>?</p>
  
  <p><strong>lldb version</strong>: lldb-320.4.115.3</p>
  
  <p><strong>g++ version</strong>: <code>Configured with: --prefix=/Applications/Xcode6-Beta5.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
  Apple LLVM version 6.0 (clang-600.0.45.3) (based on LLVM 3.5svn)
  Target: x86_64-apple-darwin13.3.0
  Thread model: posix</code></p>