C++: Provide fallbacks for missing stoi/stod functions

Notably, Android does not provide these functions.  The fallback
implementation is based on the one in the GNU ISO C++ Library.

bindings/cxx/ConfigKey_methods.cpp

@@ -30,6 +30,46 @@ const ConfigKey *ConfigKey::get(string identifier)
 	return get(info->key);
 }
 
+#include "config.h"
+
+#ifndef HAVE_STOI_STOD
+
+/* Fallback implementation of stoi and stod */
+
+#include <cstdlib>
+#include <cerrno>
+#include <stdexcept>
+#include <limits>
+
+static inline int stoi( const std::string& str )
+{
+	char *endptr;
+	errno = 0;
+	const long ret = std::strtol(str.c_str(), &endptr, 10);
+	if (endptr == str.c_str())
+		throw std::invalid_argument("stoi");
+	else if (errno == ERANGE ||
+		 ret < std::numeric_limits<int>::min() ||
+		 ret > std::numeric_limits<int>::max())
+		throw std::out_of_range("stoi");
+	else
+		return ret;
+}
+
+static inline double stod( const std::string& str )
+{
+	char *endptr;
+	errno = 0;
+	const double ret = std::strtod(str.c_str(), &endptr);
+	if (endptr == str.c_str())
+		throw std::invalid_argument("stod");
+	else if (errno == ERANGE)
+		throw std::out_of_range("stod");
+	else
+		return ret;
+}
+#endif
+
 Glib::VariantBase ConfigKey::parse_string(string value) const
 {
 	GVariant *variant;

configure.ac

@@ -386,6 +386,19 @@ PKG_CHECK_MODULES([glibmm], [glibmm-2.4 >= 2.32.0],
 	CXXLIBS="$CXXLIBS $glibmm_LIBS"],
 	[BINDINGS_CXX="no"; cxx_msg="glibmm required"])
 
+# C++ bindings want stoi and stod
+if test "x$BINDINGS_CXX" == "xyes"; then
+	AC_LANG_PUSH([C++])
+	AC_MSG_CHECKING([for stoi and stod])
+	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <string>],
+					   [{ return std::stoi("1")+std::stod("1.0"); }])],
+	       [AC_MSG_RESULT([yes]);
+		AC_DEFINE_UNQUOTED(HAVE_STOI_STOD, [1],
+		[Specifies whether we have the stoi and stod functions.])],
+	       [AC_MSG_RESULT([no])])
+	AC_LANG_POP([C++])
+fi
+
 # PyGObject is needed for the Python bindings.
 PKG_CHECK_MODULES([pygobject], [pygobject-3.0 >= 3.0.0],
         [CXXFLAGS="$CXXFLAGS $pygobject_CFLAGS";