fix: Dont' scroll after writing last row.

kilo.c

@@ -1,9 +1,11 @@
 /*** includes ***/
 
+#include <asm-generic/ioctls.h>
 #include <ctype.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/ioctl.h>
 #include <termios.h>
 #include <unistd.h>
 
@@ -13,7 +15,13 @@
 
 /*** data ***/
 
-struct termios orig_termios;
+struct editorConfig {
+    int screenrows;
+    int screencols;
+    struct termios orig_termios;
+};
+
+struct editorConfig E;
 
 /*** terminal ***/
 
@@ -28,16 +36,16 @@ void die(const char* s) {
 }
 
 void disableRawMode() {
-    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &orig_termios) == -1)
+    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &E.orig_termios) == -1)
         die("tcsetattr");
 }
 
 void enableRawMode() {
-    if (tcgetattr(STDIN_FILENO, &orig_termios) == -1)
+    if (tcgetattr(STDIN_FILENO, &E.orig_termios) == -1)
         die("tcgetattr");
     atexit(disableRawMode);
 
-    struct termios raw = orig_termios;
+    struct termios raw = E.orig_termios;
 
     raw.c_iflag &= ~(BRKINT | ICRNL | INPCK | ISTRIP | IXON);
     raw.c_oflag &= ~(OPOST);
@@ -63,11 +71,59 @@ char editorReadKey() {
     return c;
 }
 
+int getCursorPosition(int *rows, int *cols) {
+    if (write(STDOUT_FILENO, "\x1b[6n", 4) != 4) {
+        return -1;
+    }
+
+    char buf[32];
+    unsigned int i = 0;
+    // Leave space for null terminator.
+    while (i < sizeof(buf) - 1) {
+        if (read(STDIN_FILENO, &buf[i], 1) != 1)
+            break;
+        if (buf[i] == 'R')
+            break;
+        i++;
+    }
+    buf[i] = '\0';
+
+    if (buf[0] != '\x1b' || buf[1] != '[')
+        return -1;
+    if (sscanf(&buf[2], "%d;%d", rows, cols) != 2)
+        return -1;
+
+    return 0;
+}
+
+int getWindowSize(int *rows, int *cols) {
+    struct winsize ws;
+
+    if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1 || ws.ws_col == 0) {
+        // Fallback if ioctl can't query size:
+        // Move cursor to the bottom right;
+        if (write(STDOUT_FILENO, "\x1b[999C\x1b[999B", 12) != 12) {
+            return -1;
+        }
+        // then query its position.
+        return getCursorPosition(rows, cols);
+    }
+
+    *rows = ws.ws_row;
+    *cols = ws.ws_col;
+    return 0;
+}
+
 /*** output ***/
 
 void editorDrawRows() {
-    for (int y = 0; y < 24; y++) {
+    for (int y = 0; y < E.screenrows; y++) {
-        write(STDOUT_FILENO, "~\r\n", 3);
+        write(STDOUT_FILENO, "~", 1);
+
+        // Don't scroll on the last line.
+        if (y < E.screenrows - 1) {
+            write(STDOUT_FILENO, "\r\n", 2);
+        }
     }
 }
 
@@ -101,8 +157,15 @@ void editorProcessKeypress() {
 
 /*** init ***/
 
+void initEditor() {
+    if (getWindowSize(&E.screenrows, &E.screencols) == -1) {
+        die("getWindowSize");
+    }
+}
+
 int main() {
     enableRawMode();
+    initEditor();
 
     while(1) {
         editorRefreshScreen();