close_code.h: #error if included without matching begin_code.h

include/close_code.h

@@ -26,6 +26,9 @@
  *  after you finish any function and structure declarations in your headers
  */
 
+#ifndef _begin_code_h
+#error close_code.h included without matching begin_code.h
+#endif
 #undef _begin_code_h
 
 /* Reset structure packing at previous byte alignment */