If the length of the target area is larger than the length of the source, then spare space within the target area is padded with the fill character.
If the length of the target area is larger than the length of the source, then spare space within the target area is padded with the fill character.
如果目标区域的宽度大于拷贝数据的宽度，那么余下的区域将用填充字符进行填充。