How to get a FILE pointer from a file descriptor?

Question

I'm playing around with mkstemp(), which provides a file descriptor, but I want to generate formatted output via fprintf(). Is there an easy way to transform the file descriptor provided by mkstemp() into a FILE * structure that is suitable for use with fprintf()?

Answer 1

Use fdopen():

FILE* fp = fdopen(fd, "w");

Answer 2

FILE* f = fdopen(d, "w");

man fdopen output:

SYNOPSIS

#include <stdio.h>

FILE *
fdopen(int fildes, const char *mode);

The fdopen() function associates a stream with the existing file descriptor, fildes. The mode of the stream must be compatible with the mode of the file descriptor. When the stream is closed via fclose(3), fildes is closed also.

Answer 3

There is no standard way of doing this (or the reverse) as the C Standard has nothing to say about file descriptors. Your specific platform may or may not provide such a mechanism.