C++: Disable old style cast warnings in CMake - c++

Question

I am interfacing with an old code base which extensively uses old style casts (thousands). I am trying to disable these warnings in Cmake, but it just isn't working (I do not want to see 1000s of warnings, nor do I care to fix the root cause). To do this, I assume that I should be setting -Wno-old-style-cast. I tried doing this in 3 separate places in the CMakeLists.txt file, but to no avail. Here is the complete file:
set(example "train")
project(${example} CXX)
# Python
message(STATUS "We are going to force it to use Python 3. If you change this, you will need to remove the build folder and reload the cmake project.")
find_package(PythonLibs 3 EXACT)
find_package(PythonInterp 3 EXACT)
# PCL library
find_package(PCL 1.2 REQUIRED)
include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-old-style-cast")
set(CXX_COMMON_FLAGS "${CXX_COMMON_FLAGS} -Wno-old-style-cast")
add_executable(${example} src/${example}.cpp)
target_compile_options(${example} PUBLIC -Wno-old-style-cast)
target_link_libraries(${example} ${Boost_LIBRARIES} ${PCL_LIBRARIES} ${PYTHON_LIBRARIES})
target_include_directories(${example} PRIVATE include/ ${PYTHON_INCLUDE_DIRS})
I am compiling on Ubuntu 18.04 with GCC 7.4.0. I see thousands of errors like this:
/usr/include/python3.7m/object.h:118:49: warning: use of old-style cast [-Wold-style-cast]
#define Py_TYPE(ob) (((PyObject*)(ob))->ob_type)
EDIT:
The output of make VERBOSE=1 yields:
/usr/bin/c++ -DDISABLE_LIBUSB_1_0 -DDISABLE_PCAP -DDISABLE_PNG -DPCL_NO_PRECOMPILE=0 -DQT_CORE_LIB -DQT_GUI_LIB -DQT_NO_DEBUG -DQT_WIDGETS_LIB -Dqh_QHpointer -DvtkRenderingContext2D_AUTOINIT="1(vtkRenderingContextOpenGL2)" -DvtkRenderingCore_AUTOINIT="3(vtkInteractionStyle,vtkRenderingFreeType,vtkRenderingOpenGL2)" -isystem /usr/include/vtk-7.1 -isystem /usr/include/freetype2 -isystem /usr/include/x86_64-linux-gnu -isystem /usr/local/include/pcl-1.9 -isystem /usr/include/eigen3 -I/home/bob/Desktop/choc/include -I/usr/include/python3.7m -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++ -Wno-old-style-cast -Wno-old-style-cast -march=native -msse4.2 -mfpmath=sse -fPIC -std=gnu++14 -o CMakeFiles/train.dir/src/train.cpp.o -c /home/bob/Desktop/choc/src/train.cpp

Answer 1

Some libraries of pcl set -Wold-style-cast warnings using Diagnostic Pragmas. For this reason this warnings should appear whatever you set in you cmake configuration. Disabling it using pragmas before of including pcl headers solved the problem in my case.
#include <pcl/surface/concave_hull.h>
#ifdef __GNUC__
#pragma GCC diagnostic ignored "-Wold-style-cast"
#endif