MI_FUNC_DESC *mi_cast_get(conn, source_type, target_type, cast_status)
   MI_CONNECTION *conn;
   MI_TYPEID *source_type;
   MI_TYPEID *target_type;
   mi_char *cast_status;

conn

is a pointer to a connection descriptor established by a previous call to mi_open( ), mi_server_connect( ), or mi_server_reconnect( ).

can be a pointer to a session-duration connection descriptor established by a previous call to mi_get_session_connection( ). Use of a session-duration connection descriptor is an advanced feature of the DataBlade API.

source_type

is a pointer to the type identifier of the source data type for the cast.

target_type

is a pointer to the type identifier of the target data type for the cast.

cast_status

is a pointer to the status flag that mi_cast_get( ) sets to indicate the kind of cast function that it locates or the cause of an error.

Valid in Client LIBMI Application?	Valid in User-Defined Routine?
Yes	Yes

The mi_cast_get( ) function obtains a function descriptor for a cast function whose source and target data types the source_type and target_type arguments reference. The mi_cast_get( ) function accepts source and target data types as pointers to type identifiers. This function is one of the functions of the Fastpath interface. It is a constructor function for the function descriptor.

To obtain a function descriptor for a cast function, the mi_cast_get( ) function performs the following tasks:

1. Looks in the syscasts system catalog table for the cast function that casts from the source_type data type to the target_type data type
2. Allocates a function descriptor for the cast function and saves the routine sequence in this descriptor
3. Allocates an MI_FPARAM structure for the cast function and saves the argument and return-value information in this structure
4. Sets the cast_status output parameter to provide status information about the cast function
5. Returns a pointer to the function descriptor that it allocates for the cast function

The cast_status flag can have one of the following constant values.

Cast-Type Constant

Purpose

MI_ERROR_CAST

The mi_cast_get( ) function failed.

MI_NO_CAST

A cast exists between the two specified types. The user must write a function to perform the cast.

MI_NOP_CAST

A cast is not needed between the two types. The user can cast directly without a cast function.

MI_SYSTEM_CAST

A built-in cast exists to cast between two data types, usually built-in data types.

MI_EXPLICIT_CAST

A user-defined cast function exists to cast between the two types, and the cast is explicit.

MI_IMPLICIT_CAST

A user-defined cast function exists to cast between the two types, and the cast is implicit.

The following call to mi_cast_get( ) looks for a cast function that converts from the INTEGER data type to an opaque data type named percent:

MI_TYPEID *src_type, *trgt_type;
mi_char cast_stat;
MI_FUNC_DESC *func_desc;
MI_CONNECTION *conn;
...
src_type = mi_typestring_to_id(conn, "INTEGER");
trgt_type = mi_typestring_to_id(conn, "percent");

func_desc = mi_cast_get(conn, &src_type, &trgt_type,
   &cast_stat);
if ( func_desc == NULL )
   {
   switch ( cast_stat )
      {
      case MI_NO_CAST:
         mi_db_error_raise(NULL, MI_EXCEPTION, 
            "No cast function found.");
         break;
      case MI_ERROR_CAST:
         mi_db_error_raise(NULL, MI_EXCEPTION, 
            "Error in mi_cast_get( ) function.");
         break;
      case MI_NOP_CAST:
         mi_db_error_raise(NULL, MI_EXCEPTION, 
            "No cast function needed.");
         break;
      ...

An MI_FUNC_DESC
pointer

is a pointer to the function descriptor of the cast function that casts from source_type to target_type.

NULL

indicates that the cast_status value is one of the following constants:

MI_ERROR_CAST

The function was not successful.

MI_NO_CAST

No matching cast function exists.

MI_NOP_CAST

No cast function is needed between the source and target data types.

See also the descriptions of mi_fparam_get( ), mi_get_session_connection( ), mi_open( ), mi_routine_end( ), mi_routine_exec( ), mi_routine_get( ), mi_server_connect( ), mi_server_reconnect( ), and mi_td_cast_get( ).