Is there a way to get the filename from a `FILE*`? [duplicate]

Answer 1

On some platforms (such as Linux), you may be able to fetch it by reading the link of /proc/self/fd/<number>, as so:

#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main(void)
{
    char path[1024];
    char result[1024];

    /* Open a file, get the file descriptor. */
    FILE *f = fopen("/etc/passwd", "r");
    int fd = fileno(f); 

    /* Read out the link to our file descriptor. */
    sprintf(path, "/proc/self/fd/%d", fd);
    memset(result, 0, sizeof(result));
    readlink(path, result, sizeof(result)-1);

    /* Print the result. */
    printf("%s\n", result);
}

This will, on my system, print out /etc/passwd, as desired.

Answer 2

It's a bit difficult, because a FILE* can read/write from a file handle which isn't associated with a named file at all (for example an unnamed pipe or a socket). You can obtain the file handle with fileno() and then there are system specific ways to learn about the file name. Here's a discussion on how to do this under Linux:

Getting Filename from file descriptor in C

and under Windows this isn't much easier either:

http://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx (as an extra step here, you use _get_osfhandle() to get the Windows file handle from the c-library file descriptor)