Trying to fix two CLang warnings

CMakeLists.txt

@@ -81,7 +81,7 @@ ELSE()
 		SET(PROFILING "-pg") #add ${PROFILING} to the CFLAGS when necessary
 		SET(EXTRA "${EXTRA} -fcolor-diagnostics") #-fapple-pragma-pack does not seems necessary; -ftrapv should be replaced by sanitize=integer
 		SET(OPTIM "${OPTIM} -flto")
-		SET(WARNINGS "${WARNINGS} -Weverything -Wno-date-time -Wno-float-equal -Wno-documentation -Wno-documentation-unknown-command -Wno-old-style-cast -Wno-padded -Wno-missing-noreturn -Wno-weak-vtables -Wno-switch-enum") #obviously, we should try to fix the warnings! Keeping in mind that some of these W are half buggy...
+		SET(WARNINGS "${WARNINGS} -Weverything -Wno-date-time -Wno-float-equal -Wno-documentation -Wno-documentation-unknown-command -Wno-old-style-cast -Wno-padded -Wno-missing-noreturn -Wno-weak-vtables -Wno-switch-enum -Wno-covered-switch-default") #obviously, we should try to fix the warnings! Keeping in mind that some of these W are half buggy...
 		SET(DEEP_WARNINGS "${DEEP_WARNINGS} -Rpass=.*")
 		SET(LEAKS_CHECK OFF CACHE BOOL "Set to ON to dynamically check for memory corruption (and do the same for applications linked with MeteoIO)")
 			IF (LEAKS_CHECK)

meteoio/plugins/ARPSIO.cc

@@ -54,7 +54,7 @@ namespace mio {
  */
 
 const double ARPSIO::plugin_nodata = -999.; //plugin specific nodata value
-const std::string ARPSIO::default_ext=".asc"; //filename extension
+const char* ARPSIO::default_ext=".asc"; //filename extension
 
 ARPSIO::ARPSIO(const std::string& configfile)
         : cfg(configfile),

meteoio/plugins/ARPSIO.h

@@ -71,7 +71,7 @@ class ARPSIO : public IOInterface {
 
 		const Config cfg;
 		static const double plugin_nodata; //plugin specific nodata value, e.g. -999
-		static const std::string default_ext;
+		static const char* default_ext;
 		std::string coordin, coordinparam, coordout, coordoutparam; //projection parameters
 		std::string grid2dpath_in, grid3dpath_in; //where are input grids stored
 		std::string ext; //file extension