获取文件*从一个std :: fstream的 [英] Getting a FILE* from a std::fstream

问题描述

是否有一个（跨平台）的方式获得从C A C FILE *手柄++的std :: fstream的？

Is there a (cross-platform) way to get a C FILE* handle from a C++ std::fstream ?

我想问的原因是因为我的C ++库接受fstreams，在一个特定的功能，我想用一个接受文件中的C库*。

The reason I ask is because my C++ library accepts fstreams and in one particular function I'd like to use a C library that accepts a FILE*.

推荐答案

简短的答案是否定的。

究其原因，是因为的std :: fstream的不需要使用 FILE * 作为其一部分它的实现。所以，即使你设法从中提取的std :: fstream的对象文件描述符和手动构建一个文件对象，那么你就会有其他的问题，因为你现在有两个缓冲对象写入同一文件描述符。

The reason, is because the std::fstream is not required to use a FILE* as part of its implementation. So even if you manage to extract file descriptor from the std::fstream object and manually build a FILE object, then you will have other problems because you will now have two buffered objects writing to the same file descriptor.

真正的问题是，为什么要在的std :: fstream的对象转换为 FILE * ？

The real question is why do you want to convert the std::fstream object into a FILE*?

虽然我不建议这样做，你可以尝试查找 funopen（）。结果
不幸的是，不是一个POSIX API（这是一个BSD扩展），所以它的便携性问题。这也可能是为什么我找不到任何人说已结束一个的std ::流像这样的对象。

Though I don't recommend it, you could try looking up funopen().
Unfortunately, this is not a POSIX API (it's a BSD extension) so its portability is in question. Which is also probably why I can't find anybody that has wrapped a std::stream with an object like this.

FILE *funopen(
              const void *cookie,
              int    (*readfn )(void *, char *, int),
              int    (*writefn)(void *, const char *, int),
              fpos_t (*seekfn) (void *, fpos_t, int),
              int    (*closefn)(void *)
             );

这允许你建立一个文件对象，并指定将被用来做实际工作的一些功能。如果你写相应的功能，你可以让他们从实际打开了该文件中的的std :: fstream的对象读取。

This allows you to build a FILE object and specify some functions that will be used to do the actual work. If you write appropriate functions you can get them to read from the std::fstream object that actually has the file open.

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