Cython：使用C ++流 [英] Cython: working with C++ streams

问题描述

问题

如何使用c ++流（如 std :: ifstream 或 ostream ）？在c ++中，您可以执行以下操作：

How does one use c++ streams (like std::ifstream or ostream) from Cython? In c++, you could do the following:

std::ofstream output { filename, std::ios::binary };
output.write(...);

你如何在Cython中实现同样的目标？

How would you achieve the same in Cython?

当前状态

我已经在Cython中包装了fstream中的结构，以便我可以在函数声明中使用它们的名称，但是很棘手部分是使用（在Cython中包装，也许）写入方法并创建流。我没有在互联网上找到任何代码示例。

I have wrapped the structures from fstream in Cython so that I can use their names in function declarations, but the tricky part is to use (wrap in Cython, perhaps) the write method and to create the streams. I haven't found any code examples on the internet.

P.S。
我知道一个可能的答案就是使用Python的IO，但我需要传递/返回与我正在连接的C ++代码的流。

P.S. I know one possible answer would be to just use Python's IO but I need to pass/return the streams to and from C++ code that I'm interfacing with.

这是包装流声明的代码：

This is the code that wraps the stream declarations:

cdef extern from "<iostream>" namespace "std":
    cdef cppclass basic_istream[T]:
        pass

    cdef cppclass basic_ostream[T]:
        pass

    ctypedef basic_istream[char] istream

    ctypedef basic_ostream[char] ostream

推荐答案

与包装任何其他C ++类相比，c ++ iostream没有太多特别之处。唯一棘手的一点是访问 std :: ios_base :: binary ，我告诉Cython std :: ios_base 是一个命名空间而不是一个类。

There isn't much particularly special about the c++ iostreams compared to wrapping any other C++ class. The only tricky bit was getting access to std::ios_base::binary, which I did by telling Cython that std::ios_base was a namespace and not a class.

# distutils: language = c++

cdef extern from "<iostream>" namespace "std":
    cdef cppclass ostream:
        ostream& write(const char*, int) except +

# obviously std::ios_base isn't a namespace, but this lets
# Cython generate the correct C++ code
cdef extern from "<iostream>" namespace "std::ios_base":
    cdef cppclass open_mode:
        pass
    cdef open_mode binary
    # you can define other constants as needed

cdef extern from "<fstream>" namespace "std":
    cdef cppclass ofstream(ostream):
        # constructors
        ofstream(const char*) except +
        ofstream(const char*, open_mode) except+

def test_ofstream(str s):
    cdef ofstream* outputter
    # use try ... finally to ensure destructor is called
    outputter = new ofstream("output.txt",binary)
    try:
        outputter.write(s,len(s))
    finally:
        del outputter

要添加的另一件事是我没有使用完整的模板化类heirarchy - 如果你还想要 wchar可能会有用变体，但只告诉Cython你实际使用的类更容易。

The other thing to add is that I haven't bothered with the full templated class heirarchy - that might be useful if you also want the wchar variants, but it's much easier to only tell Cython about the classes you're actually using.

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