cmake: allow choice of cxx version

CMakeLists.txt

@@ -22,6 +22,10 @@ set(OVM_ENABLE_UNITTESTS ${OVM_STANDALONE_BUILD} CACHE BOOL "Build OpenVolumeMes
 set(OVM_ENABLE_EXAMPLES ${OVM_STANDALONE_BUILD} CACHE BOOL "Build OpenVolumeMesh examples in 'all' target")
 set(OVM_BUILD_DOCUMENTATION ${OVM_STANDALONE_BUILD} CACHE BOOL "Build OpenVolumeMesh documentation in 'all' target")
 
+set(OVM_CXX_VERSION 14 CACHE STRING "C++ version to use")
+set_property(CACHE OVM_CXX_VERSION PROPERTY STRINGS 14 17 20)
+
+
 if (CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
     if (WIN32)
         set (ACG_PROJECT_LIBDIR "lib")

examples/CMakeLists.txt

@@ -9,10 +9,11 @@ add_executable(simple_mesh simple_mesh/simple_mesh.cc)
 
 target_link_libraries(simple_mesh OpenVolumeMesh::OpenVolumeMesh)
 
-set_target_properties(simple_mesh PROPERTIES
-    CXX_STANDARD 14
+set_target_properties (simple_mesh PROPERTIES
+    CXX_STANDARD ${OVM_CXX_VERSION}
     CXX_STANDARD_REQUIRED YES
-    CXX_EXTENSIONS NO)
+    CXX_EXTENSIONS NO
+)
 
 #[[=
 if(WIN32)

src/CMakeLists.txt

@@ -111,7 +111,7 @@ generate_export_header(OpenVolumeMesh
 set_target_properties (OpenVolumeMesh PROPERTIES
     VERSION ${OpenVolumeMesh_VERSION_MAJOR}.${OpenVolumeMesh_VERSION_MINOR}
     SOVERSION ${OpenVolumeMesh_VERSION_MAJOR}.${OpenVolumeMesh_VERSION_MINOR}
-    CXX_STANDARD 14
+    CXX_STANDARD ${OVM_CXX_VERSION}
     CXX_STANDARD_REQUIRED YES
     CXX_EXTENSIONS NO
     CXX_VISIBILITY_PRESET hidden

src/FileConverter/CMakeLists.txt

@@ -11,21 +11,15 @@ if(Boost_FOUND)
 
   # Add target for first example
   add_executable(file_converter EXCLUDE_FROM_ALL ovm_converter.cc)
-  add_dependencies(file_converter OpenVolumeMesh)
+  set_target_properties (file_converter PROPERTIES
+      CXX_STANDARD ${OVM_CXX_VERSION}
+      CXX_STANDARD_REQUIRED YES
+      CXX_EXTENSIONS NO
+    )
+  target_link_libraries(file_converter OpenVolumeMesh)
 
   if(NOT WIN32)
-
-      # Link against all necessary libraries
-      target_link_libraries(file_converter OpenVolumeMesh)
-
-      # Set output directory to ${BINARY_DIR}/FileConverter
       set_target_properties(file_converter PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/FileConverter)
-
-  else()
-
-      # Link against all necessary libraries
-      target_link_libraries(file_converter OpenVolumeMesh)
-
   endif()
 
 else()

src/Unittests/CMakeLists.txt

@@ -31,7 +31,12 @@ if(GTEST_FOUND)
         DESTINATION "${CMAKE_BINARY_DIR}/Unittests"
         )
 
-    set_target_properties(unittests PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/Unittests)
+    set_target_properties(unittests PROPERTIES
+        RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/Unittests
+        CXX_STANDARD ${OVM_CXX_VERSION}
+        CXX_STANDARD_REQUIRED YES
+        CXX_EXTENSIONS NO
+        )
 
     #[[=
     if ( WIN32 )