title: Error in sysconf() in C++
body: <p>I am compiling a program which gives me the following error. The version of gcc is (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4.</p>
  
  <pre><code>Utils.cpp: In static member function ‘static double Utils::process_mem_usage()’:
  Utils.cpp:33:30: error: ‘_SC_PAGE_SIZE’ was not declared in this scope
    long page_size_kb = sysconf(_SC_PAGE_SIZE) / 1024; // if x86-64 is configured to use 2MB pages
                                ^
  Utils.cpp:33:43: error: ‘sysconf’ was not declared in this scope
    long page_size_kb = sysconf(_SC_PAGE_SIZE) / 1024; // if x86-64 is configured to use 2MB pages
  </code></pre>