Merge pull request #67 from chaorunrun/compile-for-c++17

Fix errors on compilation with c++17

CMakeLists.txt

@@ -45,12 +45,10 @@ endif()
 # Using span from std
 if (NOT UUID_USING_CXX20_SPAN)
     target_include_directories(${PROJECT_NAME} INTERFACE
-            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/gsl>
-            $<INSTALL_INTERFACE:include/gsl>)
-    if(UUID_ENABLE_INSTALL)
+            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+            $<INSTALL_INTERFACE:include>)
     install(DIRECTORY gsl DESTINATION include)
 endif ()
-endif ()
 
 if(UUID_ENABLE_INSTALL)
     # Install step and imported target

include/uuid.h

@@ -16,7 +16,21 @@
 #include <chrono>
 #include <numeric>
 #include <atomic>
+
+#ifdef __cplusplus
+
+#  if (__cplusplus >= 202002L) || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
+#    define LIBUUID_CPP20_OR_GREATER
+#  endif
+
+#endif
+
+
+#ifdef LIBUUID_CPP20_OR_GREATER
 #include <span>
+#else
+#include <gsl/span>
+#endif
 
 #ifdef _WIN32