SWIG Python和C：参数 [英] SWIG with python and C: arguments

问题描述

我有这个功能：

void func(int* a, int b);

这我想在蟒蛇可以像这样：

Which I want to make available in python like so:

func(list, int)

即，用户通过列表和一个整数（告诉多少项应该被存储在列表中的功能）。要做到这一点，我需要知道在初始化为AB的值（因为我需要一个原始的C的int数组暂时）。

ie, the user passes a list and an integer (telling the functions how many entries should be stored in the list). To do this, I need to know the value of "b" in the initialization for "a" (because I need a raw C int array temporarily).

%typemap(in) ( int* a) {

//need to allocate sizeof(int) * b bytes temporarily

 }

但我不知道B的价值，因为它只是在后来解析！

But I don't know the value of "b" because it is only parsed later!

我怎样才能访问B参数的值？

How can I access the value of the "b" argument?

推荐答案

您可以使用多参数类型映射。

You can use a multi-argument typemap.

%typemap(in) (const int *a, int b) %{
    $2 = (int)PyList_Size($input);
    $1 = new int[$2];
    for(Py_ssize_t i = 0; i < $2; ++i)
        $1[i] = PyLong_AsLong(PyList_GET_ITEM($input,i));
%}

%typemap(freearg) (const int* a, int b) %{
    delete [] $1;
%}

这是假设你是路过的在列表（因此 const int的* ）。因为Python列表知道它的大小，没有必要通过的大小为好。还注意到没有错误在上述的例子检查

This assumes you are passing in a list (hence the const int*). Since a Python list knows its size there is no need to pass the size as well. Also note there is no error checking in the above example.

有了这个，你传递一个Python对象（$输入）两个参数。 B （$ 2）的大小和 A （$ 1）分配一个新的 INT初始化数组的大小。数组的元素被复制到该阵列

With this you pass one Python object ($input) for the two parameters. b ($2) is initialized with the size and a ($1) allocates a new int array of that size. The elements of the array are copied to this array.

的 freearg 类型映射为函数被调用后清理。

The freearg typemap provides the cleanup after the function is called.

您使用它是这样的：

func([1,2,3,4,5])

如果您想返回一个列表，下面可以用：

If you want to return a list, the following can be used:

%typemap(in) (int *a, int b) %{
    $2 = (int)PyLong_AsLong($input);
    $1 = new int[$2];
%}

%typemap(argout) (int *a, int b) (PyObject* tmp) %{
    tmp = PyList_New($2);
    for(Py_ssize_t i = 0; i < $2; ++i)
        PyList_SET_ITEM(tmp, i, PyLong_FromLong($1[i]));
    $result = SWIG_Python_AppendOutput($result, tmp);
%}

%typemap(freearg) (int* a, int b) %{
    delete [] $1;
%}

请注意非const 为int * A 。 Python不需要的列表作为输入参数，返回一个，所以输入类型映射只是期望的整数（为简洁起见检查删除错误）。该argout类型映射构建一个Python列表出来的价值回报，并将其追加到输出结果。

Note non-const int *a. Python doesn't need a list as an input parameter to return one, so the input typemap just expects an integer (error checking removed for brevity). The argout typemap builds a Python list out of the values return and appends them to the output result.

使用这样的：

func(5)     # returns for example [1,2,3,4,5]

如果 FUNC 有返回值将返回 [RETVAL，[1,2,3,4,5]

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