Is the length of the data in the program variable, not including the length of any length indicator or terminator. Setting cbData to SQL_NULL_DATA indicates all rows copied to the server contain a NULL value for the column. Setting it to SQL_VARLEN_DATA indicates that a string terminator or other method is used to determine the length of data copied. If both a length indicator and a terminator exist, the system uses whichever one results in less data being copied.
Is the ordinal position of the column in the table to which the data is copied. The first column is 1. The ordinal position of a column is reported by SQLColumns.
The bcp_collen function allows you to change the data length in the program variable for a particular column when copying data to SQL Server with bcp_sendrow.
Initially, the data length is determined when bcp_bind is called. If the data length changes between calls to bcp_sendrow and no length prefix or terminator is being used, you can call bcp_collen to reset the length. The next call to bcp_sendrow uses the length set by the call to bcp_collen.
You must call bcp_collen once for each column in the table whose data length you want to modify.