GCC 4.9.0 is now available, with further improved C++11 and C++14 conformance.

GCC 4.9.0 Released

by Jakub Jelinek

From the announcement:

Support for various C++14 additions have been added to the C++ Front End, on the standard C++ library side the most important addition is support for the C++11 <regex>. ...

Various kinds of undefined behaviors in programs can be now diagnosed at runtime through Undefined Behavior Sanitizer. ...

See http://gcc.gnu.org/gcc-4.9/changes.html for more information about changes in GCC 4.9.

From the Changes page:

The G++ implementation of C++1y return type deduction for normal functions has been updated to conform to N3638, the proposal accepted into the working paper. Most notably, it adds decltype(auto) for getting decltype semantics rather than the template argument deduction semantics of plain auto:

int& f();
         auto  i1 = f(); // int
decltype(auto) i2 = f(); // int&

G++ supports C++1y lambda capture initializers:

[x = 42]{ ... };

Actually, they have been accepted since GCC 4.5, but now the compiler doesn't warn about them with -std=c++1y, and supports parenthesized and brace-enclosed initializers as well.

G++ supports C++1y variable length arrays. G++ has supported GNU/C99-style VLAs for a long time, but now additionally supports initializers and lambda capture by reference. In C++1y mode G++ will complain about VLA uses that are not permitted by the draft standard, such as forming a pointer to VLA type or applying sizeof to a VLA variable. Note that it now appears that VLAs will not be part of C++14, but will be part of a separate document and then perhaps C++17.

void f(int n) {
  int a[n] = { 1, 2, 3 }; // throws std::bad_array_length if n < 3
  [&a]{ for (int i : a) { cout << i << endl; } }();
  &a; // error, taking address of VLA
}

G++ supports the C++1y [[deprecated]] attribute modulo bugs in the underlying [[gnu::deprecated]] attribute. Classes and functions can be marked deprecated and a diagnostic message added:

class A;
int bar(int n);
#if __cplusplus > 201103
class [[deprecated("A is deprecated in C++14; Use B instead")]] A;
[[deprecated("bar is unsafe; use foo() instead")]]
int bar(int n);

int foo(int n);
class B;
#endif
A aa; // warning: 'A' is deprecated : A is deprecated in C++14; Use B instead
int j = bar(2); // warning: 'int bar(int)' is deprecated : bar is unsafe; use foo() instead

G++ supports C++1y digit separators. Long numeric literals can be subdivided with a single quote ' to enhance readability:

int i = 1048576;
int j = 1'048'576;
int k =0x10'0000;
int m = 0'004'000'000;
int n = 0b0001'0000'0000'0000'0000'0000;

double x = 1.602'176'565e-19;
double y = 1.602'176'565e-1'9;

G++ supports C++1y polymorphic lambdas.

// a functional object that will increment any type
auto incr = [](auto x) { return x++; };

Runtime Library (libstdc++)

Improved support for C++11, including:

• support for <regex>;
• The associative containers in <map> and <set> and the unordered associative containers in <unordered_map> and <unordered_set> meet the allocator-aware container requirements;

Improved experimental support for the upcoming ISO C++ standard, C++14, including:

• fixing constexpr member functions without const;
• implementation of the std::exchange() utility function;
• addressing tuples by type;
• implemention of std::make_unique;
• implemention of std::shared_lock;
• making std::result_of SFINAE-friendly;
• adding operator() to integral_constant;
• adding user-defined literals for standard library types std::basic_string, std::chrono::duration, and std::complex;
• adding two range overloads to non-modifying sequence oprations std::equal and std::mismatch;
• adding IO manipulators for quoted strings;
• adding constexpr members to <utility>, <complex>, <chrono>, and some containers;
• adding compile-time std::integer_sequence;
• adding cleaner transformation traits;
• making <functional>s operator functors easier to use and more generic;

An implementation of std::experimental::optional.

An implementation of std::experimental::string_view.

The non-standard function std::copy_exception has been deprecated and will be removed in a future version. std::make_exception_ptr should be used instead.