python 用 Cython 包装 C++ lib
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Wrap C++ lib with Cython
提问by YuQing Zhang
I'm new to Cython and I'm trying to use Cython to wrap a C/C++ static library. I made a simple example as follow.
我是 Cython 的新手，我正在尝试使用 Cython 来包装 C/C++ 静态库。我做了一个简单的例子如下。
Test.h:
测试.h：
#ifndef TEST_H
#define TEST_H
int add(int a, int b);
int multipy(int a, int b);
#endif
Test.cpp
测试文件
#include "test.h"
int add(int a, int b)
{
return a+b;
}
int multipy(int a, int b)
{
return a*b;
}
Then I used g++ to compile and build it.
然后我用 g++ 来编译和构建它。
g++ -c test.cpp -o libtest.o
ar rcs libtest.a libtest.o
So now I got a static library called libtest.a.
所以现在我得到了一个名为libtest.a.
Test.pyx:
测试.pyx：
cdef extern from "test.h":
int add(int a,int b)
int multipy(int a,int b)
print add(2,3)
Setup.py:
安装程序.py：
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
ext_modules = [Extension("test",
["test.pyx"],
language='c++',
include_dirs=[r'.'],
library_dirs=[r'.'],
libraries=['libtest']
)]
setup(
name = 'test',
cmdclass = {'build_ext': build_ext},
ext_modules = ext_modules
)
The I called:
我打电话给：
python setup.py build_ext --compiler=mingw32 --inplace
The output was:
输出是：
running build_ext
cythoning test.pyx to test.cpp
building 'test' extension
creating build
creating build\temp.win32-2.6
creating build\temp.win32-2.6\Release
C:\Program Files\pythonxy\mingw\bin\gcc.exe -mno-cygwin -mdll -O -Wall -I. -IC:\
Python26\include -IC:\Python26\PC -c test.cpp -o build\temp.win32-2.6\Release\test.o
writing build\temp.win32-2.6\Release\test.def
C:\Program Files\pythonxy\mingw\bin\g++.exe -mno-cygwin -mdll -static --entry _D
llMain@12 --output-lib build\temp.win32-2.6\Release\libtest.a --def build\temp.w
in32-2.6\Release\test.def -s build\temp.win32-2.6\Release\test.o -L. -LC:\Python
26\libs -LC:\Python26\PCbuild -ltest -lpython26 -lmsvcr90 -o test.pyd
g++: build\temp.win32-2.6\Release\libtest.a: No such file or directory
error: command 'g++' failed with exit status 1
I also tried to use libraries=['test']instead of libraries=['libtest']. It gave me the same errors.
我也尝试使用libraries=['test']代替libraries=['libtest']. 它给了我同样的错误。
Any clue about this?
关于这个的任何线索？
回答by Luper Rouch
If your C++ code is only used by the wrapper, another option is to let the setup compile your .cpp file, like this:
如果您的 C++ 代码仅由包装器使用，另一种选择是让安装程序编译您的 .cpp 文件，如下所示：
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
ext_modules = [Extension("test",
["test.pyx", "test.cpp"],
language='c++',
)]
setup(
name = 'test',
cmdclass = {'build_ext': build_ext},
ext_modules = ext_modules
)
For linking to a static library you have to use the extra_objectsargument in your Extension:
要链接到静态库，您必须在以下文件中使用extra_objects参数Extension：
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
ext_modules = [Extension("test",
["test.pyx"],
language='c++',
extra_objects=["libtest.a"],
)]
setup(
name = 'test',
cmdclass = {'build_ext': build_ext},
ext_modules = ext_modules
)
回答by lothario
Your Test.pyxfile isn't doing what you expect. The print add(2,3)line will notcall the add()C++ function; you have to explicitly create a wrapper function to do that. Cython doesn't create wrappers for you automatically.
您的Test.pyx文件没有按照您的预期运行。该print add(2,3)行不会调用add()C++ 函数；你必须显式地创建一个包装函数来做到这一点。Cython 不会自动为您创建包装器。
Something like this is probably what you want:
这样的事情可能是你想要的：
cdef extern from "test.h":
int _add "add"(int a,int b)
int _multiply "multiply"(int a,int b)
def add(a, b):
return _add(a, b)
def multiply(a, b):
return _multiply(a, b)
print add(2, 3)
You can look at Cython's documentationfor more details.
您可以查看 Cython 的文档以获取更多详细信息。
回答by Alex Martelli
I think you can fix this specific problem by specifying the right library_dirs(where you actually putlibtest.a -- apparently it's not getting found), but I think then you'll have another problem -- your entry points are not properly declared as extern "C", so the function's names will have been "mangled" by the C++ compiler (look at the names exported from your libtest.a and you'll see!), so any other language except C++ (including C, Cython, etc) will have problems getting at them. The fix is to declare them as extern "C".
我认为您可以通过指定正确的library_dirs（您实际放置libtest.a 的位置 - 显然没有找到）来解决这个特定问题，但我认为您会遇到另一个问题 - 您的入口点没有正确声明为extern "C"，因此函数的名称将被 C++ 编译器“修改”（查看从 libtest.a 导出的名称，您会看到！），因此除 C++ 之外的任何其他语言（包括 C、Cython 等）都会出现问题接近他们。解决方法是将它们声明为extern "C".
