future (future_error(error_code)): Construct base class with error_code's message.

	* include/std/future (future_error(error_code)): Construct base
	class with error_code's message.
	* src/c++11/future.cc (future_error::what()): Do not call c_str() on
	temporary string.

From-SVN: r221236

libstdc++-v3/ChangeLog

+2015-03-06  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/future (future_error(error_code)): Construct base
+	class with error_code's message.
+	* src/c++11/future.cc (future_error::what()): Do not call c_str() on
+	temporary string.
+
 2015-03-05  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/bits/locale_conv.h (wstring_convert::_M_conv): Handle

libstdc++-v3/include/std/future

@@ -98,7 +98,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   public:
     explicit future_error(error_code __ec)
-    : logic_error("std::future_error"), _M_code(__ec)
+    : logic_error("std::future_error: " + __ec.message()), _M_code(__ec)
     { }
 
     virtual ~future_error() noexcept;

libstdc++-v3/src/c++11/future.cc

@@ -75,7 +75,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   future_error::~future_error() noexcept { }
 
   const char*
-  future_error::what() const noexcept { return _M_code.message().c_str(); }
+  future_error::what() const noexcept { return logic_error::what(); }
 
 #if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1) \
   && (ATOMIC_INT_LOCK_FREE > 1)