Can a C fstream be Constructed from a POSIX File Descriptor?

How to Construct a C fstream from a POSIX File Descriptor?

Understanding the Dilemma

Constructing a C fstream from a POSIX file descriptor appears straightforward, yet it proves to be a complex challenge. The question arises: is this perceived simplicity a misconception or a genuinely convoluted process?

Possible Solutions and Considerations

1. Non-Standard Library Extensions:

According to the accepted answer by Éric Malenfant, accessing a POSIX file descriptor via fstream may not be possible in standard C . However, specific implementations of the standard library, such as libstdc , may offer non-standard extensions that allow this functionality. For instance, libstdc provides a fstream constructor that accepts a file descriptor as an input.

2. Custom Solutions Using Non-Standard File Handling:

Alternatively, custom solutions can be implemented. For libstdc , the __gnu_cxx::stdio_filebuf class template can be utilized. This template inherits from std::basic_streambuf and possesses a constructor that associates a file stream buffer with an open POSIX file descriptor. This buffer can then be assigned to an istream object to facilitate operations on the file.

3. Microsoft Visual C Implementation:

Microsoft Visual C offers a non-standard constructor for ifstream that accepts a FILE parameter. Although this constructor is undocumented, it enables the creation of an ifstream object from a C stream obtained using "_fdopen" to convert a POSIX file handle to a FILE.

Conclusion:

The construction of a C fstream from a POSIX file descriptor is feasible with certain caveats. The lack of explicit support in the standard library necessitates utilizing non-standard extensions or custom solutions. The most suitable approach depends on the specific platform and compiler used.

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