cmake: enable C++11 implicitly

Author: alalek

cmake/templates/OpenCVConfig.cmake.in

@@ -273,6 +273,32 @@ endif()
 # ==============================================================
 set(OpenCV_LIBRARIES ${OpenCV_LIBS})
 
+# Require C++11 features for OpenCV modules
+if(CMAKE_VERSION VERSION_LESS "3.1")
+  if(NOT OpenCV_FIND_QUIETLY AND NOT OPENCV_HIDE_WARNING_COMPILE_FEATURES)
+    message(STATUS "OpenCV: CMake version is low (${CMAKE_VERSION}, required 3.1+). Can't enable C++11 features: https://github.com/opencv/opencv/issues/13000")
+  endif()
+else()
+  set(__target opencv_core)
+  if(TARGET opencv_world)
+    set(__target opencv_world)
+  endif()
+  set(__compile_features cxx_std_11)  # CMake 3.8+
+  if(DEFINED OPENCV_COMPILE_FEATURES)
+    set(__compile_features ${OPENCV_COMPILE_FEATURES})  # custom override
+  elseif(CMAKE_VERSION VERSION_LESS "3.8")
+    set(__compile_features cxx_auto_type cxx_rvalue_references cxx_lambdas)
+  endif()
+  if(__compile_features)
+    # Simulate exported result of target_compile_features(opencv_core PUBLIC ...)
+    set_target_properties(${__target} PROPERTIES
+        INTERFACE_COMPILE_FEATURES "${__compile_features}"
+    )
+  endif()
+  unset(__target)
+  unset(__compile_features)
+endif()
+
 #
 # Some macros for samples
 #

samples/CMakeLists.example.in

@@ -12,11 +12,6 @@ file(TO_CMAKE_PATH "${EXAMPLE_FILE}" EXAMPLE_FILE)
 message(STATUS "Project: ${EXAMPLE_NAME}")
 message(STATUS "File   : ${EXAMPLE_FILE}")
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
-
 # Define project name
 project(${EXAMPLE_NAME})
 

samples/CMakeLists.txt

@@ -58,10 +58,6 @@ else()
 #===================================================================================================
 cmake_minimum_required(VERSION 3.1)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 project(samples C CXX)
 option(BUILD_EXAMPLES "Build samples" ON)
 

samples/android/face-detection/jni/CMakeLists.txt

@@ -1,9 +1,5 @@
 cmake_minimum_required(VERSION 3.6)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 set(target detection_based_tracker)
 project(${target} CXX)
 

samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt

@@ -1,9 +1,5 @@
 cmake_minimum_required(VERSION 3.6)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 set(target mixed_sample)
 project(${target} CXX)
 

samples/android/tutorial-4-opencl/jni/CMakeLists.txt

@@ -1,9 +1,5 @@
 cmake_minimum_required(VERSION 3.6)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 set(target mixed_sample)
 project(${target} CXX)
 

samples/cpp/example_cmake/CMakeLists.txt

@@ -1,10 +1,6 @@
 # cmake needs this line
 cmake_minimum_required(VERSION 3.1)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 # Define project name
 project(opencv_example_project)