C++和Python混合编程 - C++写python扩展
早就听说过了对于复杂的系统一般会结合多种语言进行开发，最近摸索了下C++和Python混合编程，在此总结一下，做为笔记。
对于C++和python混合编程实际上包含两部分内容：
- 用C++写python扩展（extending）: 即所谓的在python中调用C/C++代码，一般用于对效率要求高核心模块用C/C++编写，通过一些处理后生成动态库如cppmod.so,然在python代码中import cppmod，即可调用C/C++
- python脚本嵌入到C++程序中(embedding): 即所谓的C++代码调用python,C++ app要嵌入python解析器从而调用python代码
就实现而言，对于这两者都可以直接用Python/C API,具体可以去参考python文档，但都比较麻烦
- 对于1， 主要的方案有 boost.python 以及swig, 后者不太了解，本篇主要讲利用boost.python，对C/C++处理后生成动态库，python导入后调用C/C++代码
- 对于2， C/C++代码中嵌入python,也可以用 boost.python，当然直接 Python/C API也可以
##一、安装boost(latest version boost1.55.0)
[tanli@p04bc boost_1_55_0]$./bootstrap.sh --with-python=/usr/bin/python2.7 --with-python-root=/usr --with-python-version=2.7
[tanli@p04bc boost_1_55_0]$./b2 variant=debug link=static threading=multi --with-python
这里为节省时间，只编译boost.python库的static-debug-multi版本，默认在当前目录构建，生成的静库文件位于./statge， 构建完成好了看到信息如下：
The Boost C++ Libraries were successfully built!
The following directory should be added to compiler include paths:
/home/tanli/soft/boost_1_55_0
The following directory should be added to linker library paths:
/home/tanli/soft/boost_1_55_0/stage/lib
注意: boost.python 库是和python版本相关的，当安装Boost, 会自动探测Python版本, 如果有多个python版本，还是需要指定的，否则后面出现一些错误。
##二、用boost.python库导出C++函数
在cpp文件中增加导出接口代码
#include <iostream>
#include <boost/python.hpp>
using namespace boost::python;
void SayHello()
{
std::cout<<"hello, world!"<<std::endl;
}
void SayBye()
{
std::cout<<"good bye!"<<std::endl;
}
BOOST_PYTHON_MODULE(hello) // generate python module hello
{
def("SayHello", SayHello);
def("SayBye", SayBye);
}
编译成动态库:
[tanli@p04bc boost_1_55_0]$ g++ hello.cpp -shared -fPIC -o hello.so -I ~/soft/boost_1_55_0 -L ~/soft/boost_1_55_0/stage/lib -lboost_python -I /usr/include/python2.7
/usr/bin/ld: /home/tanli/soft/boost_1_55_0/stage/lib/libboost_python.a(registry.o): relocation R_X86_64_32 against `a local symbol' can not be used when making a shared object; recompile with -fPIC
/home/tanli/soft/boost_1_55_0/stage/lib/libboost_python.a: could not read symbols: Bad value
collect2: ld returned 1 exit status
原来是boost.python静态库有问题，要加编译选项-fPIC, 看来得改编译选项，google了下，可以怎么改 针对boost_1_55_0版本，修改tools/build/v2/tools/gcc.jam，注释掉391行：
#if $(link) = shared
按照上面命令重新编译boost.python库，然后在编译上面程序，这回好了,再打开python导入动态库调用吧
[tanli@p04bc boostpython]$g++ hello.cpp -shared -fPIC -o hello.so -I ~/soft/boost_1_55_0 -L ~/soft/boost_1_55_0/stage/lib -lboost_python -I /usr/include/python2.7
[tanli@p04bc boostpython]$python
Python 2.7 (r27:82500, Oct 20 2010, 13:31:35)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import hello
>>> hello.SayHello()
hello, world!
>>> hello.SayBye()
good bye!
>>> exit()
##三、用boost.python库导出C++类
刚才的例子是导出一个函数给python用，那么对于class呢？
#include <string>
#include <boost/python.hpp>
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
using namespace std;
class CHello{
public:
string GetString()
{
return "CHello::GetString()";
}
int GetInt()
{
return 100;
}
};
BOOST_PYTHON_MODULE(hello_class)
{
using namespace boost::python;
class_<CHello>("CHello")
.def("GetString",&CHello::GetString)
.def("GetInt",&CHello::GetInt)
;
}
编译运行：
[tanli@p04bc boostpython]$ g++ helloclass.cpp -shared -fPIC -o hello_class.so -I ~/soft/boost_1_55_0 -L ~/soft/boost_1_55_0/stage/lib -lboost_python -I /usr/include/python2.7
[tanli@p04bc boostpython]$python
Python 2.7 (r27:82500, Oct 20 2010, 13:31:35)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import hello_class
>>> a = hello_class.CHello()
>>> a.Get
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'CHello' object has no attribute 'Get'
>>> a.GetString()
'CHello::GetString()'
>>> a.GetInt()
100
>>> quit()
##四、用boost.python库导出构造函数
对于非默认构造函数怎么导出呢：
#include <string>
#include <boost/python.hpp>
using namespace std;
class CHello{
public:
CHello(string msg)
: m_msg(msg)
{
m_id = 0;
}
CHello(int id)
{
m_id = id;
}
string GetString() const
{
return m_msg;
}
string SetString(string msg)
{
m_msg = msg;
}
int GetInt()
{
return m_id;
}
int SetInt(int id)
{
m_id = id;
}
string m_msg;
int m_id;
};
BOOST_PYTHON_MODULE(hello_class)
{
using namespace boost::python;
class_<CHello>("CHello", init<string>())
.def(init<int>())
.def("SetString", &CHello::SetString)
.def("GetString", &CHello::GetString)
.def("GetInt", &CHello::GetInt)
;
}
测试结果：
[tanli@p04bc boostpython]$g++ helloclass.cpp -shared -fPIC -o hello_class.so -I ~/soft/boost_1_55_0 -L ~/soft/boost_1_55_0/stage/lib -lboost_python -I /usr/include/python2.7
[tanli@p04bc boostpython]$python
Python 2.7 (r27:82500, Oct 20 2010, 13:31:35)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import hello_class
>>> a = hello_class.CHello()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
Boost.Python.ArgumentError: Python argument types in
CHello.__init__(CHello)
did not match C++ signature:
__init__(_object*, int)
__init__(_object*, std::string)
>>> a = hello_class.CHello(1)
>>> a.GetInt()
1
>>> b = hello_class.CHello("hello world!")
>>> b.GetString()
'hello world!'
##五、总结
总的来说就是在C++里引入导出接口代码，然后生成动态库，python里以导入模块的方式加载动态库，然后调用C++程序，更多复杂的导出， 比如继续，虚函数，还是参考手册吧，这里就不介绍了。
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