How Can I Construct a C fstream from a POSIX File Descriptor?

Constructing a C fstream from a POSIX File Descriptor

Problem:
Constructing an fstream object directly from a POSIX file descriptor can be challenging in C .

Solution:

Libstd

For libstdc , there is no standard way to do this. However, libstdc offers a non-standard constructor for fstream that takes a file descriptor input.

Example:

#include <ext>
using namespace std;

int main() {
  int posix_handle = open("file.txt", O_RDONLY);  // Open a file with POSIX handle
  __gnu_cxx::stdio_filebuf<char> filebuf(posix_handle, ios::in);  // Create stdio_filebuf from POSIX handle
  ifstream ifs(&filebuf);  // Create ifstream from stdio_filebuf

  // Read from the file
}</char></ext>

Microsoft Visual C

Microsoft Visual C also provides a non-standard constructor for ifstream that accepts a FILE pointer. You can call _fdopen to obtain the FILE from the POSIX file descriptor.

Example:

#include <cstdio>
#include <fstream>
using namespace std;

FILE *_file = fopen("file.txt", "r");  // Open a file with C file handle
ifstream ifs(_fdopen(_fileno(_file), "r"));  // Create ifstream from FILE*

// Read from the file</fstream></cstdio>

Note:

These non-standard constructors may not be available in all C implementations. It is recommended to check the documentation for your specific implementation.

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