这是因为dtcopy和dt都引用相同的对象.
使用 DataTable.Copy方法 [

This is because both dtcopy and dt are referencing the same object.
Use DataTable.Copy Method[^] to copy from one datatable to another.

Instead of

dtcopy=dt;

使用

Use

dtcopy = dt.Copy();

复制数据表.

如果只需要数据表的结构而不是数据，则可以使用 DataTable.Clone方法 [^ ]

to copy the data table.

If you want only the structure of datatable and not the data you can use DataTable.Clone Method[^]