python - 如何在 cython 中制作从 C struct 到 int 的 C++ 映射？

Question

如何在 cython 中创建从 C struct 到 int 的 C++ 映射？

我试试下面的代码:

主要.py

#!/usr/bin/env python
# encoding: utf-8
import pyximport


pyximport.install()
from foo import Fun

Fun()

foo.pyx

#!/usr/bin/env python
# encoding: utf-8
from libcpp.map cimport map
from libcpp.string cimport string

cdef struct mystruct:
    int i


def Fun():
    cdef:
        map[mystruct,int] dDict
        mystruct A

    A.i=1

    dDict[A]=1

配置文件foo.pyxbld

def make_ext(modname, pyxfilename):
    from distutils.extension import Extension
    return Extension(name=modname,
                     sources=[pyxfilename],
                     language='C++')

运行 main.py 时出现以下错误:

foo.cpp
C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\xlocale(342) : warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\functional(143) : error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'const __pyx_t_3foo_mystruct'
        C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\string(150) : see declaration of 'std::operator <'
        C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\functional(142) : while compiling class template member function 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const'
        with
        [
            _Ty=__pyx_t_3foo_mystruct
        ]
        C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\map(68) : see reference to class template instantiation 'std::less<_Ty>' being compiled
        with
        [
            _Ty=__pyx_t_3foo_mystruct
        ]
        C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\xtree(22) : see reference to class template instantiation 'std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,_Mfl>' being compiled
        with
        [
            _Kty=__pyx_t_3foo_mystruct,
            _Ty=int,
            _Pr=std::less<__pyx_t_3foo_mystruct>,
            _Alloc=std::allocator<std::pair<const __pyx_t_3foo_mystruct,int>>,
            _Mfl=false
        ]
        C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\xtree(63) : see reference to class template instantiation 'std::_Tree_nod<_Traits>' being compiled
        with
        [
            _Traits=std::_Tmap_traits<__pyx_t_3foo_mystruct,int,std::less<__pyx_t_3foo_mystruct>,std::allocator<std::pair<const __pyx_t_3foo_mystruct,int>>,false>
        ]
        C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\INCLUDE\xtree(89) : see reference to class template instantiation 'std::_Tree_ptr<_Traits>' being compiled
        with
        [
            _Traits=std::_Tmap_traits<__pyx_t_3foo_mystruct,int,std::less<__pyx_t_3foo_mystruct>,std::al

我应该如何正确初始化和使用这个映射？预先感谢您的帮助!

Answer 1

能够使用键类型为 mystruct 的映射，您需要为 mystruct 定义一个比较运算符对象。实际上，C++ 映射是有序映射(通常由一些自动平衡树支持，例如 AVL 或红黑)。一个正确的语法是

cdef cppclass mystruct:
    int i
    bint lessthan "operator<"(const mystruct t) const:
         return this.i < t.i   

编辑:替换了i < t.i通过 this.i < t.i因为这更明确(Python之禅)。