Thread: Get stdin contents without newline, then replace

Don't try to grab the user input line-by-line, but by character-by-character. Yes, this means you'll have to handle stuff like backspace, delete, and character insertion yourself. It's not difficult, however:

Code:

#define   NCURSES_WIDECHAR 1
#include <locale.h>
#include <string.h>
#include <wchar.h>
#include <time.h>
#include <ncursesw/curses.h>

size_t unicode_to_utf8(char *const utf8, const size_t max,
                       const int *const unicode, const size_t unicode_len)
{
    const int           *src = unicode;
    const int *const     end = unicode + unicode_len;
    unsigned char *const dst = (unsigned char *const)utf8;
    size_t               len = 0;

    while (src < end)
        if (*src > 0 && *src < 0x80) {
            if (len < max)     dst[len] = *src;
            len += 1;
            src++;
        } else
        if (*src >= 0x80 && *src < 0x800) {
            if (len + 0 < max) dst[len + 0] = 0xC0 | ((*src >> 6) & 0x1F);
            if (len + 1 < max) dst[len + 1] = 0x80 | ((*src)      & 0x3F);
            len += 2;
            src++;
        } else
        if (*src >= 0x800 && *src < 0x10000) {
            if (len + 0 < max) dst[len + 0] = 0xE0 | ((*src >> 12) & 0x0F);
            if (len + 1 < max) dst[len + 1] = 0x80 | ((*src >>  6) & 0x3F);
            if (len + 2 < max) dst[len + 2] = 0x80 | ((*src)       & 0x3F);
            len += 3;
            src++;
        } else
        if (*src >= 0x10000 && *src < 0x200000) {
            if (len + 0 < max) dst[len + 0] = 0xF0 | ((*src >> 18) & 0x07);
            if (len + 1 < max) dst[len + 1] = 0x80 | ((*src >> 12) & 0x3F);
            if (len + 2 < max) dst[len + 2] = 0x80 | ((*src >>  6) & 0x3F);
            if (len + 3 < max) dst[len + 3] = 0x80 | ((*src)       & 0x3F);
            len += 4;
            src++;
        } else {
            /* Skip invalid code points. */
            src++;
        }

    /* Append EOS. */
    if (len < max)
        dst[len] = '\0';
    else
    if (max > 0)
        dst[max - 1] = '\0';

    return len;
}

int main()
{
    WINDOW *chat_window;
    WINDOW *input_window;
    time_t  now, then;
    wint_t  c;
    int     t, in_key, in_char;
    int     line_buf[1024], line_len, line_pos;
    char    line_str[4 * sizeof line_buf / sizeof line_buf[0]];
    size_t  line_strlen;

    /* Enable wide character support. */
    setlocale(LC_ALL, "");

    /* Start curses mode. */
    initscr();

    /* No line buffering. */
    raw();

    /* No echoing keypresses to the screen. */
    noecho();

    /* Reserve five lines for the input window. */
    chat_window = newwin(LINES - 5, COLS, 0, 0);
    input_window = newwin(5, COLS, LINES - 5, 0);

    /* The main loop will quit with F4. */
    wclear(chat_window);
    scrollok(chat_window, 1);
    wprintw(chat_window, "Press F4 or CTRL+Q or CTRL+W to quit.");
    wrefresh(chat_window);

    /* Show the input prompt. */
    wclear(input_window);
    wprintw(input_window, "> ");

    /* wget_wch() returns ERR if there is no key pressed. */
    nodelay(input_window, TRUE);

    /* We want F1 et cetera. */
    keypad(input_window, TRUE);

    /* No input line yet. */
    line_len = 0;
    line_pos = 0;
    now = time(NULL);

    while (1) {
        int changes = 0;
        int cx, cy;

        /* Check for pending chat messages. */
        then = now;
        now = time(NULL);
        if (then != now) {
            wprintw(chat_window, "\n\rTick tock.");
            changes = 1;
        }

        /* Check for user input. */
        t = wget_wch(input_window, &c);
        if (t == KEY_CODE_YES) {
            in_key = c;
            in_char = 0;
        } else
        if (t == OK) {
            in_key = 0;
            in_char = c;
        } else {
            in_key = 0;
            in_char = 0;
        }

        /* F4, Ctrl-Q, and Ctrl-C quit. */
        if (in_key == KEY_F(4) || in_char == 3 || in_char == 17)
            break;

        /* Terminal window resized? */
        if (in_key == KEY_RESIZE) {
            wresize(chat_window, LINES - 5, COLS);
            wresize(input_window, 5, COLS);
            mvwin(input_window, LINES - 5, 0);
            changes = 1;
        }

        /* Cursor movement left and right. */
        if (in_key == KEY_LEFT && line_pos > 0) {
            line_pos--;
            changes = 1;
        } else
        if (in_key == KEY_RIGHT && line_pos < line_len) {
            line_pos++;
            changes = 1;
        }

        /* Up/Down == Home/End */
        if (in_key == KEY_UP || in_key == KEY_HOME) {
            line_pos = 0;
            changes = 1;
        } else
        if (in_key == KEY_DOWN || in_key == KEY_END) {
            line_pos = line_len;
            changes = 1;
        }

        /* Backspace deletes the previous character. */
        if (in_key == KEY_BACKSPACE || in_char == '\b') {
            if (line_pos > 0) {
                if (line_len > line_pos)
                    memmove(line_buf + line_pos - 1, line_buf + line_pos, (line_len - line_pos) * sizeof line_buf[0]);
                line_pos--;
                line_len--;
            }
            changes = 1;
        }

        /* Delete deletes the next character. */
        if (in_key == KEY_DC || in_char == 127) {
            if (line_pos < line_len) {
                if (line_pos + 1 < line_len)
                    memmove(line_buf + line_pos, line_buf + line_pos + 1, (line_len - line_pos - 1) * sizeof line_buf[0]);
                line_len--;
            }
            changes = 1;
        }

        /* Enter submits the string. */
        if (in_key == KEY_ENTER || in_char == '\n') {
            line_strlen = unicode_to_utf8(line_str, sizeof line_str, line_buf, line_len);
            if (line_strlen > 0) {
                /*
                 * TODO: Send line_str (contains line_strlen bytes).
                */
                wprintw(chat_window, "\n\rMe: %s", line_str);
            }
            line_len = 0;
            line_pos = 0;
            changes = 1;
        }

        /* New character. */
        if (in_char >= 32 && line_len < (int)(sizeof line_buf / sizeof line_buf[0])) {
            if (line_pos < line_len)
                memmove(line_buf + line_pos + 1, line_buf + line_pos, (line_len - line_pos) * sizeof line_buf[0]);
            line_buf[line_pos] = in_char;
            line_pos++;
            line_len++;
            changes = 1;
        }

        /* If any changes, refresh output. */
        if (changes) {
            wrefresh(chat_window);

            wclear(input_window);
            wprintw(input_window, "> ");

            if (line_pos > 0) {
                line_strlen = unicode_to_utf8(line_str, sizeof line_str, line_buf, line_pos);
                wprintw(input_window, "%s", line_str);
            }
            if (line_len > line_pos) {
                getyx(input_window, cy, cx); /* Macro, not a function. Modifies cx and cy! */
                line_strlen = unicode_to_utf8(line_str, sizeof line_str, line_buf + line_pos, line_len - line_pos);
                wprintw(input_window, "%s", line_str);
                wmove(input_window, cy, cx);
            }

            wrefresh(input_window);
        }
    }

    /* End curses mode. */
    endwin();

    return 0;
}

If you save the above as chat-example.c, you can compile and run it using

Code:

gcc -Wall -O2 chat-example.c -lncursesw -o chat-example
./chat-example

Make sure you have libncurses5w-dev or libncurses-devel packages installed.

The above example uses wide character input, and assumes curses provides the keys as unicode code points. An int array is used to store the "string" currently being modified. When needed for output or printing, the unicode_to_utf8() function is used to convert the code points to an UTF-8 string. (Note that the resulting string can be at most four bytes per code point, plus one byte for the end-of-string mark, long.)

The current input line is printed in two parts: first, up to current cursor position (line_pos), followed by the rest of the line (from line_pos to line_len), with the cursor repositioned into the middle if the second part was printed. That way the cursor should appear in the correct location.

I don't have Windows, so I cannot check what modifications (aside from the include line) are needed for PDCurses. It might just work as-is, or it might only work for ASCII characters.

If I were you, I'd consider writing an AJAX interface to your chat server, either as a CGI program, or by extending your chat server to a full HTTP/1.0 service. That way you could use your chat daemon via any browser, as long as the server runs on a machine that you can connect to.

Very solid and thorough answer Nominal, thanks. Worked great.