Question

My C/C++ program takes a file from the command line as an argument. Reading data from ‘regular files’ is no problem/general programming task, but when the file comes from a ‘device pipe’ such as /dev/fd/63 it causes my program to crash.

To reproduce:

from your friendly neighborhood bash shell supply a ‘device pipe’ as a file to your application. Your app should try to read the file contents into a buffer.

./yourapp <(echo ‘Hello World!’); # /dev/fd/xx containing output from echo command.

Note the above command is not redirecting the standard input of the application and that is not the intended result..

I don’t think that a lot of people know this will crash their application. The application ‘seed’ from the Gnome project uses glib to do its I/O but it can read from these files just fine. The command ‘cat’ can also handle this situation gracefully. Why is it when I try to read the contents of that named pipe like a regular file my application gets the crash bug?

EDIT: relavent code section

#include <stdio.h>

int main(int argc, char **argv) {

    FILE *file;

    char *buffer;

    unsigned long fileLen;

    //Open file
    file = fopen(argv[1], "rb");
    if (!file) return -1;

    //Get file length
    fseek(file, 0, SEEK_END);
    fileLen=ftell(file);

    fseek(file, 0, SEEK_SET);

    //Allocate memory
    buffer=(char *)malloc(fileLen+1);

    if (!buffer){
        fprintf(stderr, "Memory error!");
        fclose(file);
        return -2;
    }

    //Read file contents into buffer
    fread(buffer, fileLen, 1, file);
    fclose(file);

    fprintf(stdout, "Size: %i", fileLen);

    free(buffer);

}

Answer 1

Can’t call fseek on a pipe. The code shows that I was indeed trying to do such a foolish thing.