Distinguishing a pipe from a file in Unix

Question

Given a FILE*, is it possible to determine the underlying type? That is, is there a function that will tell me if the FILE* is a pipe or a socket or a regular on-disk file?

Answer 1

There's a fstat(2) function.

NAME stat, fstat, lstat - get file status

SYNOPSIS

   #include <sys/types.h>
   #include <sys/stat.h>
   #include <unistd.h>

   int fstat(int fd, struct stat *buf);

You can get the fd by calling fileno(3).

Then you can call S_ISFIFO(buf) to figure it out.

Answer 2

Use the fstat() function. However, you'll need to use the fileno() macro to get the file descriptor from file FILE struct.

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

FILE *fp = fopen(path, "r");
int fd = fileno(fp);
struct stat statbuf;

fstat(fd, &statbuf);

/* a decoding case statement would be good here */
printf("%s is file type %08o\n", path, (statbuf.st_mode & 0777000);