问题:如何正确包装 std::vectorstd::size_t 与 Python 的 SWIG? std::size_t 的问题

我试图让std::vector<std::size_t>与 SWIG 一起工作。我需要为 c++ 库提供一个 python 接口。std::vectors 的原始类型和对象工作正常,但std::size_t存在问题。

我在这里](https://github.com/paulbible/swig_std_size_t)在 github[上提供了一个 MCVE。

主要问题

基本上问题是std::size_t未被识别,std::vector<std::size_t>被视为std::vector< int,std::allocator< int > > *。当我尝试指定模板时,我得到以下信息。

使用%template(VecSize) std::vector<std::size_t>;给出:

swig -c++ -python c_swig_vec_std_size.i
:0: Warning(490): Fragment 'SWIG_AsVal_std_size_t' not found.
:0: Warning(490): Fragment 'SWIG_From_std_size_t' not found.
g++ -fpic -c c_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
c_swig_vec_std_size_wrap.cxx: In static member function ‘static int swig::traits_asval<long unsigned int>::asval(PyObject*, swig::traits_asval::value_type*)’:
c_swig_vec_std_size_wrap.cxx:4289: error: ‘SWIG_AsVal_std_size_t’ was not declared in this scope
c_swig_vec_std_size_wrap.cxx: In static member function ‘static PyObject* swig::traits_from<long unsigned int>::from(const swig::traits_from::value_type&)’:
c_swig_vec_std_size_wrap.cxx:4295: error: ‘SWIG_From_std_size_t’ was not declared in this scope
make: *** [c] Error 1

最小示例

示例 c++ 类

下面的类足以显示我需要的功能。包含std::vector<int>以显示预期的行为。

类_vec_std_size.hpp

#ifndef STD_SIZE_VEC
#define STD_SIZE_VEC

#include <vector>

class StdSizeVec{

public:
  StdSizeVec(){
    _myVec = std::vector<std::size_t>();
    _myVec.push_back(1);
    _myVec.push_back(2);

    _myInts = std::vector<int>();
    _myInts.push_back(1);
    _myInts.push_back(2);
  }

  ~StdSizeVec(){
    _myVec.clear();
  }

  inline std::vector<std::size_t> getValues(){
    return _myVec;
  }

  inline std::vector<int> getInts(){
    return _myInts;
  }

private:
  std::vector<std::size_t> _myVec;
  std::vector<int> _myInts;
};
#endif

界面的各种尝试

a_swig_vec_std_size.i

%module a_swig_vec_std_size
%{
#include "class_vec_std_size.hpp"
%}
%include "class_vec_std_size.hpp"

输出

[paul@login-0-0 stack_swig]$ python
Python 2.7.11 (default, May  7 2016, 23:37:19) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-16)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from a_swig_vec_std_size import StdSizeVec
>>> ssv = StdSizeVec()
>>> vals = ssv.getValues()
>>> vals
<Swig Object of type 'std::vector< std::size_t > *' at 0x2ad7047be330>
>>> ints = ssv.getInts()
>>> ints
<Swig Object of type 'std::vector< int > *' at 0x2ad7047be780>
>>> exit()
swig/python detected a memory leak of type 'std::vector< int > *', no destructor found.
swig/python detected a memory leak of type 'std::vector< std::size_t > *', no destructor found.
[paul@login-0-0 stack_swig]$

这是基本的幼稚方法。指针在 python 中没有用,并且存在我们无法向接口用户公开的内存泄漏消息。

b_swig_vec_std_size.i

%module b_swig_vec_std_size
%{
#include "class_vec_std_size.hpp"
%}
%include "std_vector.i"
%include "class_vec_std_size.hpp"

输出

[paul@login-0-0 stack_swig]$ python
Python 2.7.11 (default, May  7 2016, 23:37:19) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-16)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from b_swig_vec_std_size import StdSizeVec
>>> ssv = StdSizeVec()
>>> vals = ssv.getValues()
>>> vals
<Swig Object of type 'std::vector< std::size_t,std::allocator< std::size_t > > *' at 0x2aee17458330>
>>> ints = ssv.getInts()
>>> ints
<Swig Object of type 'std::vector< int,std::allocator< int > > *' at 0x2aee17458930>
>>> exit()
swig/python detected a memory leak of type 'std::vector< int,std::allocator< int > > *', no destructor found.
swig/python detected a memory leak of type 'std::vector< std::size_t,std::allocator< std::size_t > > *', no destructor found.

使用正确的“std_vector.i”,SWIG 对向量和分配器有更多了解,但这些指针仍然对 python 中的客户端代码没有用,并且存在内存泄漏错误消息。

c_swig_vec_std_size.i

该接口使用正确的%template指令,例如这个答案。这里 SWIG 不将std::size_t理解为模板参数。

%module c_swig_vec_std_size
%{
#include "class_vec_std_size.hpp"
%}
%include "std_vector.i"
%template(VecInt) std::vector<int>;

// Does not compile
//%template(VecSize) std::vector<std::size_t>;
//
// Gives the following errors
//swig -c++ -python c_swig_vec_std_size.i
// :0: Warning(490): Fragment 'SWIG_AsVal_std_size_t' not found.
// :0: Warning(490): Fragment 'SWIG_From_std_size_t' not found.
// g++ -fpic -c c_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
// c_swig_vec_std_size_wrap.cxx: In static member function ‘static int swig::traits_asval<long unsigned int>::asval(PyObject*, swig::traits_asval::value_type*)’:
// c_swig_vec_std_size_wrap.cxx:4289: error: ‘SWIG_AsVal_std_size_t’ was not declared in this scope
// c_swig_vec_std_size_wrap.cxx: In static member function ‘static PyObject* swig::traits_from<long unsigned int>::from(const swig::traits_from::value_type&)’:
// c_swig_vec_std_size_wrap.cxx:4295: error: ‘SWIG_From_std_size_t’ was not declared in this scope
// make: *** [c] Error 1

//The following compiles but does not work
%template(VecSize) std::vector<size_t>;

%include "class_vec_std_size.hpp"

输出

[paul@login-0-0 stack_swig]$ python
Python 2.7.11 (default, May  7 2016, 23:37:19) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-16)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from c_swig_vec_std_size import StdSizeVec
>>> ssv = StdSizeVec()
>>> vals = ssv.getValues()
>>> vals
<Swig Object of type 'std::vector< std::size_t,std::allocator< std::size_t > > *' at 0x2b286104bd80>
>>> ints = ssv.getInts()
>>> ints
(1, 2)
>>> exit()
swig/python detected a memory leak of type 'std::vector< std::size_t,std::allocator< std::size_t > > *', no destructor found.

现在std::vector<int>工作正常,但 SWIG 的%template(VecSize) std::vector<size_t>;(没有std::)不能完成这项工作。

一些网络挖掘

我发现了一些提供一些线索的帖子。

感觉像这个我找到了一个2006的帖子,同样的问题

std::vector::size_type 包装为指针而不是整数链接有一些有用的信息,但问题并不完全相同。

我从 magnum.fe 项目中找到了这个primitives.i,但是一厢情愿地思考并导入 primitives.i 对我不起作用。

之后,我尝试实现类似于他们的方法的SWIG_AsVal_std_size_t和SWIG_From_std_size_t,但没有运气。

手卷std_size_t.i

%fragment("SWIG_From_std_size_t", "header", fragment=SWIG_From_frag(std::size_t))
{
  SWIGINTERNINLINE PyObject * SWIG_From_std_size_t(std::size_t value)
  {
    return PyInt_FromSize_t(value);
  }
}


%fragment("SWIG_AsVal_std_size_t", "header")
{

SWIGINTERNINLINE bool SWIG_AsVal_std_size_t(PyObject* in, std::size_t& value)
{

  // Get integer type
  if(PyInt_Check(in)){
    long unsigned int long_uint = PyLong_AsLong(in);
    value = static_cast<std::size_t>(long_uint);
    return true;
  }else{
    return false;
  }

}
}

%fragment(SWIG_From_frag(std::size_t));
%fragment("SWIG_AsVal_std_size_t");

这是在 d_swig_vec_std_size.i 中导入的。但它不编译。

%module d_swig_vec_std_size
%{
#include "class_vec_std_size.hpp"
%}
%include "std_vector.i"
%template(VecInt) std::vector<int>;

%include "std_size_t.i"
%template(VecSize) std::vector<std::size_t>;

%include "class_vec_std_size.hpp"

我明白了。

swig -c++ -python d_swig_vec_std_size.i
g++ -fpic -c d_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
d_swig_vec_std_size_wrap.cxx: In static member function ‘static int swig::traits_asval<long unsigned int>::asval(PyObject*, swig::traits_asval::value_type*)’:
d_swig_vec_std_size_wrap.cxx:4311: error: invalid initialization of reference of type ‘size_t&’ from expression of type ‘swig::traits_asval::value_type*’
d_swig_vec_std_size_wrap.cxx:4288: error: in passing argument 2 of ‘bool SWIG_AsVal_std_size_t(PyObject*, size_t&)’
make: *** [d] Error 1

生成文件

PYTHON=/public/users/paul/dev/software/Python-2.7.11

all: a b c d

a:
    swig -c++ -python a_swig_vec_std_size.i
    g++ -fpic -c a_swig_vec_std_size_wrap.cxx -I${PYTHON}/Include -I${PYTHON}
    g++ -g -fpic -shared a_swig_vec_std_size_wrap.o -o _a_swig_vec_std_size.so

b:
    swig -c++ -python b_swig_vec_std_size.i
    g++ -fpic -c b_swig_vec_std_size_wrap.cxx -I${PYTHON}/Include -I${PYTHON}
    g++ -g -fpic -shared b_swig_vec_std_size_wrap.o -o _b_swig_vec_std_size.so

c:
    swig -c++ -python c_swig_vec_std_size.i
    g++ -fpic -c c_swig_vec_std_size_wrap.cxx -I${PYTHON}/Include -I${PYTHON}
    g++ -g -fpic -shared c_swig_vec_std_size_wrap.o -o _c_swig_vec_std_size.so

d:
    swig -c++ -python d_swig_vec_std_size.i
    g++ -fpic -c d_swig_vec_std_size_wrap.cxx -I${PYTHON}/Include -I${PYTHON}
    g++ -g -fpic -shared d_swig_vec_std_size_wrap.o -o _d_swig_vec_std_size.so


clean: clean_a clean_b clean_c clean_d

clean_a:
    rm a_swig_vec_std_size_wrap.cxx a_swig_vec_std_size.py a_swig_vec_std_size_wrap.o _a_swig_vec_std_size.so

clean_b:
    rm b_swig_vec_std_size_wrap.cxx b_swig_vec_std_size.py b_swig_vec_std_size_wrap.o _b_swig_vec_std_size.so

clean_c:
    rm c_swig_vec_std_size_wrap.cxx c_swig_vec_std_size.py c_swig_vec_std_size_wrap.o _c_swig_vec_std_size.so

clean_d:
    rm d_swig_vec_std_size_wrap.cxx d_swig_vec_std_size.py d_swig_vec_std_size_wrap.o _d_swig_vec_std_size.so

程序版本

python version: Python 2.7.11
g++ version: g++ (GCC) 4.4.7
swig version: SWIG Version 1.3.40

使用较新的 swig 版本(swig-3.0.10)对我来说是相同的结果。

总结

我怀疑答案可能在某处的接口 d 中,但到目前为止我还没有运气。std::size_t的实现方式可能存在问题,具体取决于架构而不是固定大小。无论如何,我希望 SWIG 能够处理它。我错过了什么吗?我想找到一个不涉及对 C++ 库进行更改的解决方案(例如将 std::size_t 封装在struct中或改用int)。

尝试 Jens Monk 的解决方案

namespace std {
    %template(VecSize) vector<size_t>;
}

我明白了:

[paul@login-0-0 stack_swig]$ make clean
rm a_swig_vec_std_size_wrap.cxx a_swig_vec_std_size.py a_swig_vec_std_size_wrap.o _a_swig_vec_std_size.so
rm b_swig_vec_std_size_wrap.cxx b_swig_vec_std_size.py b_swig_vec_std_size_wrap.o _b_swig_vec_std_size.so
rm c_swig_vec_std_size_wrap.cxx c_swig_vec_std_size.py c_swig_vec_std_size_wrap.o _c_swig_vec_std_size.so
rm d_swig_vec_std_size_wrap.cxx d_swig_vec_std_size.py d_swig_vec_std_size_wrap.o _d_swig_vec_std_size.so
[paul@login-0-0 stack_swig]$ make
swig -c++ -python a_swig_vec_std_size.i
g++ -fpic -c a_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
g++ -g -fpic -shared a_swig_vec_std_size_wrap.o -o _a_swig_vec_std_size.so
swig -c++ -python b_swig_vec_std_size.i
g++ -fpic -c b_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
g++ -g -fpic -shared b_swig_vec_std_size_wrap.o -o _b_swig_vec_std_size.so
swig -c++ -python c_swig_vec_std_size.i
g++ -fpic -c c_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
g++ -g -fpic -shared c_swig_vec_std_size_wrap.o -o _c_swig_vec_std_size.so
swig -c++ -python -I/public/users/paul/dev/software/swig-3.0.10  d_swig_vec_std_size.i
g++ -fpic -c d_swig_vec_std_size_wrap.cxx -I/public/users/paul/dev/software/Python-2.7.11/Include -I/public/users/paul/dev/software/Python-2.7.11
g++ -g -fpic -shared d_swig_vec_std_size_wrap.o -o _d_swig_vec_std_size.so
[paul@login-0-0 stack_swig]$ python
Python 2.7.11 (default, May  7 2016, 23:37:19) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-16)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from d_swig_vec_std_size import StdSizeVec
>>> ssv = StdSizeVec()
>>> vals = ssv.getValues()
>>> vals
<Swig Object of type 'std::vector< std::size_t,std::allocator< std::size_t > > *' at 0x2aba7dd8bd80>
>>> ints - ssv.getInts()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'ints' is not defined
>>> ints = ssv.getInts()
>>> ints
(1, 2)
>>> exit()
swig/python detected a memory leak of type 'std::vector< std::size_t,std::allocator< std::size_t > > *', no destructor found.
[paul@login-0-0 stack_swig]$ cat d_swig_vec_std_size.i 
%module d_swig_vec_std_size
%{
#include "class_vec_std_size.hpp"
%}
%include "std_vector.i"
%template(VecInt) std::vector<int>;

%include "std_size_t.i"

namespace std {
  %template(VecSize) vector<size_t>;
}


%include "class_vec_std_size.hpp"

解答

尝试如下所示为 swig 定义 size_t -http://www.swig.org/Doc1.3/SWIG.html#SWIG_nn20

%inline %{
typedef long unsigned int size_t;
%}

namespace std {
  %template(VecSize) vector<size_t>;
}