pager

In this example program, it will demonstrate how ringbuffer could be implemented in a pager. User could take a sample text then point that text to this program via command argument as below

./pager Blindsight.txt

Where "Blindsight.txt" is a sample text that supplied in this repository. You can change it to any text you want.

---

main.c

 
#include <errno.h>
#include <ringbuffer.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
// Sleep function in Windows is not POSIX compliant, so we need to wrap it
#if __has_include(<windows.h>)
    #include <Windows.h>
    #define SLEEP(t) Sleep (t)
#else
    #include <unistd.h>
    #define SLEEP(t) usleep (t * 1000)
#endif
 
int
main (int arg_count, char **args)
{
    if (arg_count != 2) {
        char *exec_name = "./pager";
        if (arg_count)
            exec_name = args[0];
 
        if (arg_count > 1)
            fputs ("Wrong usage!\r\n", stderr);
        else
            fputs ("Please provide <path_to_file>\r\n", stderr);
 
        printf ("USAGE:\r\n"
                "    %s <path_to_file>\r\n",
                exec_name);
 
        return EINVAL;
    }
 
    char plain_array[80];
    ringbuffer_context_t context;
    FILE *text_file;
    int return_code = EXIT_FAILURE;
 
    if (strcmp (args[1], "-")) {
        text_file = fopen (args[1], "rt");
    } else {
        text_file = stdin;
    }
 
    if (!text_file) {
        fprintf (stderr, "Cannot open the file because '%s' reason\r\n",
                 strerror (errno));
        return errno;
    }
 
    context = ringbuffer_init (plain_array, sizeof (char), sizeof (plain_array),
                               0, 0);
    if (!context) {
        return_code = errno;
        if (return_code) {
            fprintf (stderr, "Cannot open the file because '%s' reason\r\n",
                     strerror (return_code));
            goto cleanup_after_open;
        }
 
        return_code = EXIT_FAILURE;
        fputs ("Something went wrong in ringbuffer module, please check the "
               "params\r\n",
               stderr);
        goto cleanup_after_open;
    }
 
    memset (plain_array, ' ', sizeof (plain_array));
 
    do {
        int each_letter = fgetc (text_file);
        if (each_letter == EOF) {
            if (feof (text_file))
                break;
 
            return_code = errno;
            if (return_code < 1) {
                fprintf (stderr,
                         "Failed to read \"%s\" for unknown reason\033[0K\r\n",
                         args[1]);
                return_code = EXIT_FAILURE;
                break;
            }
 
            fprintf (stderr,
                     "Failed to read \"%s\" because '%s' reason\033[0K\r\n",
                     args[1], strerror (return_code));
            break;
        }
 
        if (each_letter == '\n')
            each_letter = ' ';
        else if (each_letter < 32 || each_letter > 126)
            continue;
 
        ringbuffer_write (context, &each_letter);
 
        plain_array[ringbuffer_get_write_index (context)] = '>';
 
        printf ("%.*s\033[0K\r", (int)sizeof (plain_array), plain_array);
        fflush (stdout);
        SLEEP (100);
    } while (!feof (text_file));
 
    ringbuffer_destroy (&context);
 
    return_code = EXIT_SUCCESS;
 
cleanup_after_open:
    if (text_file != stdin)
        fclose (text_file);
 
    fputs ("\033[0K", stdout);
    fflush (stdout);
    return return_code;
}