如何取到DataTable各个列的最大长度？

[yibuyi]

为什么用col.MaxLength会得到-1?

[TheAres]

You can use the INFORMATION_SCHEMA views in SQL Server, through a regular
Command, if your database is SQL Server. Or use
OleDbConnection.GetOleDbSchemaTable with an OLE DB provider that supports
it.

Or you can do a DataAdapter.Fill with a MissingSchemaAction of
MissingSchemaAction.AddWithKey. Then refer to DataColumn.MaxLength. Or use
CommandBehavior.KeyInfo or SchemaOnly and look at the DataReader's SchemaTable.

[dahuzizyd]

DataColumns.MaxLength:列的最大长度（以字符数表示）。如果列没有最大长度，该值为 -1（默认值）。对于非文本列，则忽略 MaxLength 属性。