MySQL 5.7 C API Developer Guide
MYSQL_FIELD *
mysql_fetch_field_direct(MYSQL_RES *result,
unsigned int fieldnr)
Given a field number fieldnr for a column
within a result set, returns that column's field definition as
a MYSQL_FIELD structure. Use this function
to retrieve the definition for an arbitrary column. Specify a
value for fieldnr in the range from 0 to
mysql_num_fields(result)-1.