How Can I Get a C FILE* from a C std::fstream?

Can You Obtain a C FILE* from a C std::fstream?

Suppose you possess a C library that operates with fstreams, and for a specific function, you desire to employ a C library that utilizes a FILE*. While this aspiration may seem reasonable, it presents a significant challenge.

Unfortunately, there exists no cross-platform method to directly extract a C FILE handle from a C std::fstream. This is because the implementation of std::fstream varies across different platforms and is not required to use a FILE underneath.

Attempting to manually construct a FILE object based on the file descriptor extracted from the std::fstream would lead to further issues. Both the std::fstream and the FILE object would attempt to perform buffered writes to the same file descriptor, potentially causing conflicts and data corruption.

Therefore, it is crucial to determine why you need to convert the std::fstream object to a FILE*. Based on the specific requirements of your function, consider exploring alternative solutions such as:

• Modifying the C library function to accept an std::fstream instead of a FILE*.
• Rewriting the code that calls the C library function to use C streams.
• Employing the POSIX API to create a FILE object directly from the file descriptor.
• Utilizing the BSD extension funopen() to create a FILE object based on custom read and write functions that interface with the std::fstream.

These options can provide a more robust and platform-independent solution for your integration requirements.

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