I have a FILE returned by a call to fopen I need to get a file descriptor from it to make calls like fsync fd on it What s the function to get a file descriptor from a file pointer

The proper function is int fileno FILE stream It can be found in lt stdio h gt and is a POSIX standard but not standard C

[c] How can I convert a file pointer ( FILE* fp ) to a file descriptor (int fd)?

Even if fileno(FILE *) may return a file descriptor, be VERY careful not to bypass stdio's buffer. If there is buffer data (either read or unflushed write), reads/writes from the file descriptor might give you unexpected results.

To answer one of the side questions, to convert a file descriptor to a FILE pointer, use fdopen(3)

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