don't store the output lines in memory

Now that I understand the problem space and the C wide string APIs
better, I realize that we don't need to store the lines in memory
at all. We can just print chars directly to stdout.

src/main.c

@@ -59,27 +59,9 @@ void termput1(char *cmd, int arg1) {
  putp(tgoto(o, 0, arg1));
 }
 
-void str_append(wchar_t **line, ssize_t *len, size_t *cap, wchar_t c) {
- // Note that cap (and len) are # of wchar_t not # of bytes.
- if (*len == *cap) {
- *cap = *cap < 255 ? 255 : *cap * 2;
- *line = abort_null(realloc(*line, *cap * sizeof(wchar_t)));
- // This memset isn't strictly necessary because we zero-terminate the
- // string later. But valgrind sees uninitialized reads in printf because
- // it uses vector operators that read past the zero, so rather than add
- // suppressions I'm just zeroing all the buffer.
- memset((*line) + (*len), 0, ((*cap) - (*len)) * sizeof(wchar_t));
- }
- (*line)[(*len)++] = c;
-}
-
-// Follows the same general pattern as libc's getline(), but reads into a
-// wchar_t string and throws away the rest of the line once max_display_len is
-// reached.
-// Note this is *display* length, not character length. A single unicode character
-// doesn't always display as a single visual character on the terminal.
-// Returns the calculated display_length, or -1 on EOF/error.
-ssize_t read_line(FILE *s, wchar_t **line, size_t *cap, size_t max_display_len) {
+// Read a single line from s and print it out. Once max_display_len is reached,
+// keep scanning for the rest of the line but don't print anymore.
+ssize_t read_line(FILE *s, size_t max_display_len) {
  ssize_t display_len = 0;
  ssize_t len = 0;
  for (;;) {
@@ -91,40 +73,37 @@ ssize_t read_line(FILE *s, wchar_t **line, size_t *cap, size_t max_display_len)
  break;
  }
  if (c == L'\n') {
- // don't append the newline
  break;
  }
  int c_len = wcwidth(c);
  if ((display_len + c_len) > max_display_len) {
  continue;
  }
- str_append(line, &len, cap, c);
+ putwchar(c);
  display_len += c_len;
  }
- str_append(line, &len, cap, 0);
+ if (max_display_len > 0)
+ putwchar(L'\n');
  return display_len;
 }
 
 // Read the file stream and show the first page of output.
 void read_show_output(FILE *s, size_t *count, size_t *shown, size_t *total) {
  termput0("cd");
- wchar_t *line = NULL;
- size_t cap = 0;
+ int lines_left = LINES - 2;
  for (;;) {
- int lines_left = LINES - 2 - *shown;
  ssize_t display_len =
- read_line(s, &line, &cap, truncate_lines ? COLS : COLS * lines_left);
+ read_line(s, truncate_lines ? COLS : COLS * lines_left);
  if (display_len < 0)
  break;
  *total += 1;
- // if we haven't filled the screen yet, display this line.
  if (lines_left > 0) {
- printf("%ls\n", line);
  *count += 1;
- *shown += (int)ceil((double)display_len / COLS);
+ int nlines = (int)ceil((double)display_len / COLS);
+ lines_left -= nlines;
+ *shown += nlines;
  }
  }
- free(line);
 }
 
 // Fork the child process, run the given command in shell. Prints the first page
@@ -227,7 +206,7 @@ static struct option const long_options[] = {
 void usage(int status) {
  printf("Usage: %s [OPTIONS]\n", program_name);
  printf("\n");
- printf(" -t, --truncate Truncate long lines rather than  wrapping.\n");
+ printf(" -t, --truncate Truncate long lines rather than wrapping.\n");
  exit(status);
 }