kilo commentary: Wecome message (steps 41 and 42)

Steps 41 and 42 add a welcome message to our nascent editor implementation. It starts with another #define:

#define KILO_VERSION "0.0.1"

As I mentioned before, I'm not a fan of using the preprocessor when it can be avoided, and there's no reason not to declare this as a global character constant. But this is just awful:

void editorDrawRows(struct abuf *ab) {
  int y;
  for (y = 0; y < E.screenrows; y++) {
    if (y == E.screenrows / 3) {
      char welcome[80];
      int welcomelen = snprintf(welcome, sizeof(welcome),
        "Kilo editor -- version %s", KILO_VERSION);
      if (welcomelen > E.screencols) welcomelen = E.screencols;
      int padding = (E.screencols - welcomelen) / 2;
      if (padding) {
        abAppend(ab, "~", 1);
        padding--;
      }
      while (padding--) abAppend(ab, " ", 1);
      abAppend(ab, welcome, welcomelen);
    } else {
      abAppend(ab, "~", 1);
    }
    abAppend(ab, "\x1b[K", 3);
    if (y < E.screenrows - 1) {
      abAppend(ab, "\r\n", 2);
    }
  }
}

In a function called editorDrawRows fully half of the implementation is taken up with displaying the welcome message. We also see again the "reversed if" control flow organization:

if (condition)
  rare case
else
  usual case

I assume we'll see a lot of changes to this function as we go, but for now the implementation is greatly improved by reversing the ordering of the if statement, and moving the code to write the welcome message to its own function.

void editorDrawRows(struct abuf *ab) {
  int y;
  for (y = 0; y < E.screenrows; y++) {
    if (y != E.screenrows / 3) {
      abAppend(ab, "~", 1);
    } else {
      addWelcomeMessage(ab);
    }

    abAppend(ab, "\x1b[K", 3); /* erase to end of line */
    if (y < E.screenrows - 1) {
      abAppend(ab, "\r\n", 2);
    }
  }
}