Update cmake to cpp 17 (#511)

* Update cmake to cpp 17

* Update Cmake based on torch version

* Default cpp version 14

CMakeLists.txt

@@ -29,7 +29,9 @@ if(NOT CMAKE_BUILD_TYPE)
 endif()
 message(STATUS "CMAKE_BUILD_TYPE: ${CMAKE_BUILD_TYPE}")
 
-set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ version to be used.")
+if(NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ version to be used.")
+endif()
 set(CMAKE_CXX_EXTENSIONS OFF)
 
 option(SHERPA_ENABLE_TESTS "Whether to build tests" OFF)

cmake/cmake_extension.py

@@ -9,7 +9,7 @@
 
 import setuptools
 from setuptools.command.build_ext import build_ext
-
+import torch
 
 def is_for_pypi():
     ans = os.environ.get("SHERPA_IS_FOR_PYPI", None)
@@ -24,6 +24,11 @@ def is_windows():
     return platform.system() == "Windows"
 
 
+def get_pytorch_version():
+    # if it is 1.7.1+cuda101, then strip +cuda101
+    return torch.__version__.split("+")[0]
+
+
 try:
     from wheel.bdist_wheel import bdist_wheel as _bdist_wheel
 
@@ -77,6 +82,12 @@ def build_extension(self, ext: setuptools.extension.Extension):
             print(f"Setting PYTHON_EXECUTABLE to {sys.executable}")
             cmake_args += f" -DPYTHON_EXECUTABLE={sys.executable}"
 
+        major, minor = get_pytorch_version().split(".")[:2]
+        major = int(major)
+        minor = int(minor)
+        if major == 2 and minor >= 1:
+            extra_cmake_args += f" -DCMAKE_CXX_STANDARD=17 "
+
         cmake_args += extra_cmake_args
 
         if is_windows():