cc1plus：warning：命令行选项“-Wstrict-prototypes”适用于Ada / C / ObjC但不适用于C ++

问题描述

我正在构建一个用于Python的C ++扩展。我看到这个警告是在编译过程中产生的 - 当一个类型为：

  python setup.py build_ext -i 
  

造成这种情况的原因是什么，以及如何解决它？

顺便说一下，这是我的设置文件的副本：

 ＃！/ usr / bin / env python 
 

 setup.py文件，用于SWIG示例

 $ b $ from distutils.core import setup，Extension 
 
 
 example_module = Extension（'_ foolib'，
 sources = ['example_wrap.cxx'，
'../wrapper++/src/Foo.cpp'
]，
库= [foopp] 
）
 
 setup（name ='foolib'，
 version ='0.1'，
 author =Me，Myself and I，
 description =例子，
 ext_m odules = [example_module]，
 py_modules = [example]，
）
  

我在Ubuntu上使用gcc 4.4.3

解决方案

我可以回答部分问题，为什么你会得到消息。

构建过程中的某些内容是使用 -Wstrict-prototypes 选项在C ++源文件上调用gcc， 。对于C和Objective-C，这会导致编译器警告未声明参数类型的旧式函数声明。

对于C ++，此选项不会没有道理; （原型是强制性的）。

（我不知道为什么消息提到Ada; - Wstrict-prototypes 对于Ada而言比C ++更不明智，这不是什么大问题，但我已经提交了，截至2015-12-06标记为RESOLVED / FIXED。）

解决方案应该是删除来自调用gcc的 -Wstrict-prototypes 选项。但是，由于您不是直接调用gcc，所以很难知道如何做到这一点。

我可以使用设置重现警告.py ，手动创建一个虚拟 example_wrap.cxx 文件：

 ％python setup.py build_ext -i 
正在运行build_ext 
建立'_foolib'扩展
 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：命令行选项-Wstrict-prototypes适用于Ada / C / ObjC，但不适用于C ++ 
 ... 
  

$ b $所以它可能是Python的 build_ext 中的一个小错误。

但是，因为它只是一个警告，而不是一个致命的错误，我会说你可以放心地忽略它。 gcc对无意义的选项提出警告，但它只是忽略它。

编辑：

通过Python-2.7.2来源，这部分 configure.in 可能是罪魁祸首：

  case $ gcc in 
 yes）
 if test$ CC！='g ++';那么
 STRICT_PROTO = -  Wstrict-prototypes
 fi 
  

假设这是在使用 build_ext 时调用的。）

它打开 -Wstrict-原型选项仅当编译器 not 被调用为 g ++ - 但在你的情况下它使用 gcc 命令编译C ++源代码。并且在 Lib / distutils / command / build_ext.py 中， build_extension（）不关注源文件当调用 self.compiler.compile（）时，仅在调用 self.compiler.link_shared_object（）时使用语言。 （这看起来很奇怪;对于gcc以外的编译器，你不一定能够使用相同的命令来编译C和C ++ - 并且使用 g ++ 命令，即使你没有链接。）

更新：提交了Python错误报告：，并将其作为这一个的副本关闭：，它在我写这篇文章时仍然是打开的。

但正如我所说，这只是一个警告而你可以安全地忽略它。也许Python维护者可以使用上述信息来解决未来版本中的问题。

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

解决方案

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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