I am building a C++ extension for use in Python. I am seeing this warning being generated during the compilation process - when a type:
python setup.py build_ext -i
What is causing it, and how do I fix it?
BTW, here is a copy of my setup file:
#!/usr/bin/env python """ setup.py file for SWIG example """ from distutils.core import setup, Extension example_module = Extension('_foolib', sources=['example_wrap.cxx', '../wrapper++/src/Foo.cpp' ], libraries=["foopp"] ) setup (name = 'foolib', version = '0.1', author = "Me, Myself and I", description = """Example""", ext_modules = [example_module], py_modules = ["example"], )
I am using gcc 4.4.3 on Ubuntu
I can answer part of the question, why you're getting the message.
Something in your build process is invoking gcc on a C++ source file with the option -Wstrict-prototypes
. For C and Objective-C, this causes the compiler to warn about old-style function declarations that don't declare the types of arguments.
For C++, this option doesn't make sense; such declarations aren't even allowed by the language (prototypes are mandatory).
(I don't know why the message mentions Ada; -Wstrict-prototypes
makes even less sense for Ada than for C++. It's not a huge deal, but I've submitted this bug report, marked as RESOLVED/FIXED as of 2015-12-06.)
The solution should be to remove the -Wstrict-prototypes
option from the invocation of gcc. But since you're not invoking gcc directly, it's difficult to know how to do that.
I was able to reproduce the warning using your setup.py
, after manually creating a dummy example_wrap.cxx
file:
% python setup.py build_ext -i running build_ext building '_foolib' extension gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c example_wrap.cxx -o build/temp.linux-i686-2.7/example_wrap.o cc1plus: warning: command line option "-Wstrict-prototypes" is valid for Ada/C/ObjC but not for C++ ...
So it's probably a minor bug in Python's build_ext
.
But since it's only a warning, not a fatal error, I'd say you can safely ignore it. gcc warns about the meaningless option, but then it just ignores it.
EDIT:
Looking through the Python-2.7.2 sources, this section of configure.in
might be the culprit:
case $GCC in yes) if test "$CC" != 'g++' ; then STRICT_PROTO="-Wstrict-prototypes" fi
(I'm assuming that's invoked when using build_ext
.)
It turns on the -Wstrict-prototypes
option only if the compiler is not being invoked as g++
-- but in your case it's using the gcc
command to compile C++ source code. And in Lib/distutils/command/build_ext.py
, build_extension()
doesn't pay attention to the source file language when invoking self.compiler.compile()
, only when invoking self.compiler.link_shared_object()
. (Which seems odd; for compilers other than gcc, you wouldn't necessarily be able to use the same command to compile C and C++ -- and it makes more sense to use the g++
command anyway, even if you're not linking.)
UPDATE: A Python bug report was submitted: https://bugs.python.org/issue9031, and closed as a duplicate of this one: https://bugs.python.org/issue1222585, which is still open as I write this.
But as I said, it's only a warning and you can probably safely ignore it. Perhaps the Python maintainers can use the above information to fix the problem in a future release.
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