call it data instead of c_ptr for approaching C++11 std::vector convention.

src/math/realclosure/realclosure.h

@@ -273,7 +273,7 @@ namespace realclosure {
         num():m_value(nullptr) {}
 
         // Low level functions for implementing the C API
-        void * c_ptr() { return m_value; }
+        void * data() { return m_value; }
         static num mk(void * ptr) { num r; r.m_value = reinterpret_cast<value*>(ptr); return r; }
     };
 };