[英]Why does this extern “C” function not work using python ctypes?
I have the following c++ function that sets an integer using a string. 我有以下使用字符串设置整数的c ++函数。
#include <sstream>
#include <string>
#include <iostream>
using namespace std;
extern "C" {
int a() {
int number;
string value("100");
std::istringstream strm(value);
strm >> number;
if (strm.fail()) {
cout << "Ouch!" << endl;
}
else {
cout << "Number set to:" << number << endl;
};
return (int)strm.bad();
}
}
int main(int argc, char **argv)
{
a();
}
If I compile this as a program it works. 如果我将其作为程序进行编译,它将可以正常工作。
$ g++ ./streamtest.cc -o streamtest;./streamtest
Number set to:100
But if I call the same function from ctypes it does not set the integer and the "strm" is left in a "bad" state. 但是,如果我从ctypes调用相同的函数,它不会设置整数,并且“ strm”处于“坏”状态。
$ g++ -shared streamtest.cc -o libstreamtest.so
$ python -c "import ctypes;a = ctypes.CDLL('libstreamtest.so').a();print 'Got [%s] from a()' %a"
Ouch!
Got [1] from a()
This got me puzzled. 这让我感到困惑。 How can I make this function work under ctypes?
如何使此函数在ctypes下工作?
It works for me on Windows 7 (x64) using x86 build. 它在Windows 7(x64)上使用x86构建对我有效。 Have you tried wrapping the code with C for use as module with Python?
您是否尝试过用C封装代码以用作Python模块? Maybe that does work for you..
也许对您有用。
C:\Users\niklas\Desktop>g++ -o streamtest.pyd -shared -I"C:\Python27\include" -L"C:\Python27\libs" streamtestmodule.cpp -lpython27
C:\Users\niklas\Desktop>python
Python 2.7.2 (default, Jun 12 2011, 15:08:59) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import streamtest
>>> streamtest.a()
Number set to:100
0
#include <Python.h>
#include "streamtest.cpp"
extern "C" {
static PyObject* streamtest_a(PyObject* self) {
PyObject* re = Py_BuildValue("i", a());
return re;
}
static PyMethodDef StreamtestMethods[] = {
{"a", (PyCFunction) streamtest_a, METH_NOARGS, NULL},
{NULL, NULL, 0, NULL}
};
void initstreamtest(void) {
PyObject* module = Py_InitModule("streamtest", StreamtestMethods);
if (module == NULL) {
cout << "Module initialization failed.";
}
}
} // extern "C"
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