Improved C++11 detection.

dlib/dnn/test_for_cpp11/cpp11_test.cpp

@@ -13,15 +13,26 @@ public:
     testme(testme&&) = default;
     testme(const testme&) = delete;
 
+
+    template <typename T>
+    auto auto_return(T f) -> decltype(f(4)) { return f(4); }
+
+    template <typename T>
+    auto auto_return(T f) -> decltype(f()) { return f(); }
+
+    int returnint() { return 0; }
+
     void dostuff()
     {
-        thread_local stuff1 = 999;
+        thread_local int stuff1 = 999;
         auto x = 4;
 
         decltype(x) asdf = 9;
 
-        auto f = [](){ cout << "in a lambda!" << endl; };
+        auto f = []() { cout << "in a lambda!" << endl; };
         f();
+
+        auto_return(returnint);
     }
 
     template <typename ...T>
@@ -31,6 +42,8 @@ public:
     {
     }
 
+
+
     std::shared_ptr<int> asdf;
 };
 

dlib/use_cpp_11.cmake

@@ -24,7 +24,7 @@ include(${dlib_path}/add_global_compiler_switch.cmake)
 # Now turn on the appropriate compiler switch to enable C++11 if you have a
 # C++11 compiler.  In CMake 3.1 there is a simple flag you can set, but earlier
 # verions of CMake are not so convenient.
-if (CMAKE_VERSION VERSION_LESS "3.1")
+if (CMAKE_VERSION VERSION_LESS "3.1.2")
    if(CMAKE_COMPILER_IS_GNUCXX)
       execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION)
       if (GCC_VERSION VERSION_GREATER 4.8 OR GCC_VERSION VERSION_EQUAL 4.8)
@@ -61,6 +61,7 @@ else()
        ";${CMAKE_CXX_COMPILE_FEATURES};" MATCHES ";cxx_delegating_constructors;" AND
        ";${CMAKE_CXX_COMPILE_FEATURES};" MATCHES ";cxx_thread_local;" AND
        ";${CMAKE_CXX_COMPILE_FEATURES};" MATCHES ";cxx_constexpr;" AND
+       ";${CMAKE_CXX_COMPILE_FEATURES};" MATCHES ";cxx_decltype_incomplete_return_types;" AND
        ";${CMAKE_CXX_COMPILE_FEATURES};" MATCHES ";cxx_auto_type;")
 
       set(COMPILER_CAN_DO_CPP_11 1)