Read from stdin or multiple file arguments

Question

What my main is supposed to do is either read from stdin using system calls. Or if file arguments are given open the file arguments. I had already coded this to read from one file argument. But now I need it to open from multiple file arguments and I am short on the logic as to how to do this. How would I get my code to be able to open multiple file arguments?

int main(int argc, char *argv[]) {
    char *file_pathname = NULL;
    int fd;
    char file_buffer[540];

    //Check for proper number of arguments:
    if(argc < 2) {
        exit(2);
    }

    if(argc < 3) {
        file_pathname = "stdin";
    }

    file_pathname = argv[2];   

    if(argc < 3) {
        ((fd = read(STDIN_FILENO,file_buffer, FILE_BUFFER_SIZE)));
    }
    // FILE argument given, so try to open it:
    if (argc == 3) {
        if ((fd = open(file_pathname,O_RDONLY)) == -1) {
            perror("ERROR OPENING FILE");
            return 2;
        }

Answer 1

If you want your program run only on linux (POSIX Compatible) system you can be interested in

man 3 getopt

This is function that can help you to parse command line arguments in short unix style, for example:

myprog -a 5654 -f -n ~/Test/input.txt

There are also getopt_long() and getopt_long_only() if you want to parse long options.

If you want some specific argument parser(which i do NOT recommend), you can implement it as library.

There are glib parser if you are using glib or gtk. Or a parser in qxt (an extension Qt library) if you have a qt project. Or you can just google for more lightweight cross-platform argument parsers if you need.

Answer 2

Start with a function that gets a file descritor and does what you want:

void do_stuff(int fd);

Add another one, which does the same with a file name:

void do_stuff_fname(const char *fname);  /* Open fname and call do_stuff */

Now, your main should call either:

if (argc < 2) {
    do_stuff(STDIN_FILENO);
} else {
    int i;
    for (i=1; i<argc; i++) do_stuff_fname(argv[i]);
}

You can improve this by using getopt , as JustAnotherCurious suggested