我有一個C++類,有兩個方法(大項目的一部分)。這些方法做了一個非常類似的工作:第一個方法歸一化矢量並返回它,而第二個方法返回一個歸一化矢量,而不改變原始矢量。Python中的C++類的奇怪行爲SWIG
vector3.h
:
class Vector3
{
public:
Vector3(double a = 0.0, double b = 0.0, double c = 0.0)
: x(a), y(b), z(c) {}
Vector3(const Vector3& other) : x(other.x), y(other.y), z(other.z) {}
double length() const { return sqrt(x*x+y*y+z*z); }
Vector3& normalize()
{
float_type n = length();
n = float_type(1.0)/(n ? n : 1.0);
this->x *= n;
this->y *= n;
this->z *= n;
return *this;
}
Vector3 normalized() const
{
Vector3 v(*this);
v.normalize();
return v;
}
std::string toString()
{
std::ostringstream strm;
strm << '(' << x << ", " << y << ", " << z << ')' ;
return strm.str();
}
Vector3 operator+(const Vector3& other) const
{
return Vector3(x + other.x, y + other.y, z + other.z);
}
private:
double x,y,z;
};
我建立Python綁定這一類SWIG(通過cmake的)。
vector3.i
:
%include <stl.i>
%include <carrays.i>
%include <cpointer.i>
%module vectortest
%{
#include "vector3.h"
%}
%include "vector3.h"
CMakeLists.txt
:
cmake_minimum_required(VERSION 2.8)
add_executable("vtest" "vtest.cpp")
find_package(SWIG)
include(${SWIG_USE_FILE})
find_package(PythonLibs)
find_package(PythonInterp)
include_directories(${CMAKE_SOURCE_DIR})
include_directories(${PYTHON_INCLUDE_DIRS})
SET(CMAKE_SWIG_FLAGS "")
SET_SOURCE_FILES_PROPERTIES(SOURCE vector3.i PROPERTIES CPLUSPLUS ON)
SWIG_ADD_MODULE(vectortest_python python vector3.i)
SWIG_LINK_LIBRARIES(vectortest_python ${PYTHON_LIBRARIES} ${LIBS})
set_target_properties(_vectortest_python PROPERTIES PREFIX "_" OUTPUT_NAME "vectortest")
execute_process(COMMAND ${PYTHON_EXECUTABLE} -c "from distutils.sysconfig import get_python_lib; print (get_python_lib())" OUTPUT_VARIABLE PYTHON_SITE_PACKAGES OUTPUT_STRIP_TRAILING_WHITESPACE)
install(TARGETS ${SWIG_MODULE_vectortest_python_REAL_NAME} DESTINATION ${PYTHON_SITE_PACKAGES})
install(FILES ${CMAKE_BINARY_DIR}/vectortest.py DESTINATION ${PYTHON_SITE_PACKAGES})
在C++中的行爲是細。
vtest.cpp
:
#include <iostream>
#include "vector3.h"
int main()
{
Vector3 v1(1,0,0);
Vector3 v2(0,1,0);
std::cout << (v1+v2).toString() << std::endl;
std::cout << (v1+v2).normalized().toString() << std::endl;
std::cout << (v1+v2).normalize().toString() << std::endl;
return 0;
}
輸出:
(1, 1, 0)
(0.707107, 0.707107, 0)
(0.707107, 0.707107, 0)
然而,它在Python行爲是很奇怪:
vtest.py
:
#!/usr/bin/python3
from vectortest import Vector3
v1 = Vector3(1,0,0)
v2 = Vector3(0,1,0)
print((v1+v2).toString())
print((v1+v2).normalized().toString())
print((v1+v2).normalize().toString())
個輸出:
(1, 1, 0)
(0.707107, 0.707107, 0)
(0, 0.707107, 0)
如預期的第二種方法(normalized()
)工作,但是第一個(normalize()
)沒有。這是什麼造成的?有關如何解決此問題的任何建議?
這可能是由V1 + v2'的'早期破壞你的swigged版本 – donkopotamus
的'的Vector3造成'對象不是'C++'Vector3'對象,而是被滑動的包裝器對象。正如@donkopotamus所建議的那樣,我認爲這個對象早就被摧毀了。在調用'normalize()'之前,你有沒有試過存儲矢量'(v1 + v2)'? –
當然,存儲'v1 + v2'有助於「解決」這個問題。但據我所見,我的C++和Python代碼都是完全有效的,所以結果應該可以正確執行。它要麼是我的代碼無效,要麼是SWIG,Python或GCC中存在錯誤。後者很難,所以我做錯了什麼? –