Fix CUDA/C++14 compilation

src/CMakeLists.txt

@@ -34,7 +34,17 @@ if(IS_MSVC)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W3")
 elseif(IS_GNU OR IS_CLANG)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14 -Wall")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
+    # We want c++14 mainly for supporting latest dependencies, but older GCC
+    # versions in combination with CUDA do not yet support it. In the worst
+    # case, this will lead to compile errors and there is not much we can
+    # do on the COLMAP side.
+    if(CUDA_ENABLED AND
+       IS_GNU AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 6)
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+    else()
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
+    endif()
 endif()
 
 add_subdirectory(base)