static VALUE
strio_putc(VALUE self, VALUE ch)
{
struct StringIO *ptr = writable(StringIO(self));
int c = NUM2CHR(ch);
long olen;
check_modifiable(ptr);
olen = RSTRING_LEN(ptr->string);
if (ptr->flags & FMODE_APPEND) {
ptr->pos = olen;
}
strio_extend(ptr, ptr->pos, 1);
RSTRING_PTR(ptr->string)[ptr->pos++] = c;
OBJ_INFECT(ptr->string, self);
return ch;
}