for gcc 9.4

cmake/AddGitSubmodule.cmake

-cmake_minimum_required(VERSION 3.19)
+cmake_minimum_required(VERSION 3.16..3.19)
 
 function(add_git_submodule dir)
 	# add a Git submodule directory to CMake, assuming the
@@ -11,9 +11,14 @@ function(add_git_submodule dir)
 	find_package(Git REQUIRED)
 
 	if(NOT EXISTS ${dir}/CMakeLists.txt)
-		execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive -- ${dir}
-			WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
-			COMMAND_ERROR_IS_FATAL ANY)
+		if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.19)
+			execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive -- ${dir}
+				WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+				COMMAND_ERROR_IS_FATAL ANY)
+		else()
+			execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive -- ${dir}
+				WORKING_DIRECTORY ${PROJECT_SOURCE_DIR})
+		endif()
 	endif()
 
 	set(ENABLE_TESTING OFF)

include/cif++/model.hpp

@@ -137,7 +137,7 @@ class atom
 			{
 				auto s = get_property(name);
 
-				std::from_chars_result r = std::from_chars(s.data(), s.data() + s.length(), result);
+				std::from_chars_result r = cif::from_chars(s.data(), s.data() + s.length(), result);
 				if (r.ec != std::errc() and VERBOSE > 0)
 					std::cerr << "Error converting " << s << " to number for property " << name << std::endl;
 			}