Open FILE* using CreateFile

Question

Is there a way to create stdio's FILE* structure on the basis of a handle returned by WinAPI's CreateFile in C++?

@MatthieuBrucher , I know that at a minimum there is `_get_osfhandle()`: https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle?view=vs-2017 . So the reverse is possible: get `HANDLE` from existing `FILE*` — Serge Rogatch, Jan 21 '19 at 10:17
@MatthieuBrucher They *have* to be related. At the lowest level, a `FILE` *must* contain a `HANDLE` from `CreateFile`. (Actually, that's not quite true. It could use `NtCreateFile` - but that is vanishingly unlikely.) — Martin Bonner supports Monica, Jan 21 '19 at 10:28
@i486 , yes, I want to use stdio functions like `fscanf` and `fread`, get the stream buffering, etc. — Serge Rogatch, Jan 21 '19 at 10:30
@SergeRogatch Instead of `fread` you can use `ReadFile`. `fscanf` is not good idea but if you need `*scanf` it can be combination from `ReadFile` and `sscanf`. Or simply use `_wfopen` to get `FILE *`. — i486, Jan 21 '19 at 10:35
@i486, I can't use `_wfopen` because I need to pass some platform-specific flags to `CreateFile` . — Serge Rogatch, Jan 21 '19 at 10:40

user7860670 · Accepted Answer · 2019-01-21T10:36:47.523

Maybe like this:

#include <Windows.h>
#include <io.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>

// takes ownership of h_file
// caller is responsible for disposing of returned stream descriptor
[[nodiscard]] FILE *
make_stream(HANDLE const h_file)
{
     FILE * p_file{};
     int const fd{::_open_osfhandle(reinterpret_cast<::intptr_t>(h_file), _O_RDONLY)}; // transferring h_file ownerhip
     if(-1 != fd)
     {
          p_file = ::_fdopen(fd, "r"); // transferring fd ownerhip
          if(NULL != p_file)
          {
              // ok
          }
          else
          {
               if(-1 == ::_close(fd))
               {
                   ::abort();
               }
          }
     }
     else
     {
         if(FALSE == ::CloseHandle(h_file))
         {
             ::abort();
         }
     }
     return p_file;
}

Open FILE* using CreateFile

1 Answers1