Merge pull request #922 from atgeirr/from_char-workaround

Add workaround for libc++ incomplete from_chars().

opm/models/utils/parametersystem.hh

@@ -41,6 +41,7 @@
 #include <dune/common/classname.hh>
 #include <dune/common/parametertree.hh>
 
+#include <cstdlib>
 #include <charconv>
 #include <fstream>
 #include <iostream>
@@ -924,7 +925,18 @@ auto Get(bool errorIfNotRegistered)
         defaultValue = defVal == "1";
     }
     else {
+#ifdef _LIBCPP_VERSION // If this macro is defined, clang's libc++ is used
+        // For floating point types, libc++ (the llvm/clang library implementation)
+        // does not yet (as of clang 15) offer an implementation of std::from_chars().
+        if constexpr (std::is_integral_v<ParamType>) {
+            std::from_chars(defVal.data(), defVal.data() + defVal.size(), defaultValue);
+        } else {
+            // Floating point workaround.
+            defaultValue = std::strtod(defVal.c_str(), nullptr);
+        }
+#else
         std::from_chars(defVal.data(), defVal.data() + defVal.size(), defaultValue);
+#endif
     }
 
     // prefix the parameter name by the model's GroupName. E.g. If