struct buffer {
  char *text;
  size_t len;
  size_t allocsize;

  /* structural invariant: text[len]==0 */
};

void buffer_init(struct buffer *);
void buffer_cleanup(struct buffer *);

void buffer_append(struct buffer *, const char *);
void buffer_add(struct buffer *, int ch);
void buffer_start(struct buffer *, int ch);
void buffer_clear(struct buffer *);