Python/SWIG:输出一个数组

问题描述

我正在尝试从使用 SWIG for Python 包装的 C 函数输出一组值.我试图做的方式是使用以下类型映射.

I am trying to output an array of values from a C function wrapped using SWIG for Python. The way I am trying to do is using the following typemap.

伪代码:

int oldmain() {
float *output = {0,1};
return output;
}

字体映射:

%typemap(out) float* {
   int i;
  $result = PyList_New($1_dim0);
   for (i = 0; i < $1_dim0; i++) {
 PyObject *o = PyFloat_FromDouble((double) $1[i]);
 PyList_SetItem($result,i,o);
 }
}

我的代码编译得很好，但是当我运行访问这个函数时它挂起(没有更多的方法来调试它).

My code compiles well, but it hangs when I run access this function (with no more ways to debug it).

对我哪里出错有什么建议吗?

Any suggestions on where I am going wrong?

谢谢.

推荐答案

这应该可以帮助您:

/* example.c */

float * oldmain() {
    static float output[] = {0.,1.};
    return output;
}

您在这里返回一个指针，而 swig 不知道它的大小.普通的 $1_dim0 不起作用，所以你必须硬编码或做一些其他的魔术.像这样:

You are returning a pointer here, and swig has no idea about the size of it. Plain $1_dim0 would not work, so you would have to hard code or do some other magic. Something like this:

/* example.i */
%module example
%{
 /* Put header files here or function declarations like below */
  extern float * oldmain();
%}

%typemap(out) float* oldmain {
  int i;
  //$1, $1_dim0, $1_dim1
  $result = PyList_New(2);
  for (i = 0; i < 2; i++) {
    PyObject *o = PyFloat_FromDouble((double) $1[i]);
    PyList_SetItem($result,i,o);
  }
}

%include "example.c"

那么在python中你应该得到:

Then in python you should get:

>> import example
>> example.oldmain()
[0.0, 1.0]

添加类型映射时，您可能会发现 -debug-tmsearch 非常方便，即

When adding typemaps you may find -debug-tmsearch very handy, i.e.

swig -python -debug-tmsearch example.i

在为 float *oldmain 寻找合适的out"类型映射时，应该清楚地表明使用了您的类型映射.此外，如果您只是想访问 c 全局变量数组，您可以使用 varout 的类型映射而不是 out 来执行相同的技巧.

Should clearly indicate that your typemap is used when looking for a suitable 'out' typemap for float *oldmain. Also if you just like to access c global variable array you can do the same trick using typemap for varout instead of just out.

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