表示显示最小的位数,如果格式化后的输出小于这个长度,则用空格或0补齐长度;如果输出大于这个长度,则它不起作用。
因此输出长度不会比1小,因此这里的1不起作用。
C标准总的说明:
An optional minimum field width. If the converted value has fewer characters than the field width, it is padded with spaces (by default) on the left (or right, if the left adjustment flag, described later, has been given) to the field width.