title: error: ‘::acos’ has not been declared using ::acos;
body: <p>I encountered this error while trying to build a cpp project using CLion. Here is the error message:</p>
  
  <pre><code>/usr/include/c++/5/cmath:102:11: error: ‘::acos’ has not been declared
     using ::acos;
             ^
  /usr/include/c++/5/cmath:121:11: error: ‘::asin’ has not been declared
     using ::asin;
             ^
  /usr/include/c++/5/cmath:140:11: error: ‘::atan’ has not been declared
     using ::atan;
             ^
  /usr/include/c++/5/cmath:159:11: error: ‘::atan2’ has not been declared
     using ::atan2;
             ^
  /usr/include/c++/5/cmath:180:11: error: ‘::ceil’ has not been declared
     using ::ceil;
             ^
  /usr/include/c++/5/cmath:199:11: error: ‘::cos’ has not been declared
     using ::cos;
  
  ...
  </code></pre>
  
  <p>In the project, there is a custom header file called <code>~/someproject/src/math.h</code>. Changing the <code>~/someproject/src/math.h</code> file name to a non-conflicting name such as <code>math1.h</code> (and updating its references accordingly) resolves the error. </p>
  
  <p>Does anybody know of another solution to this that does not require a name change?</p>