The ASN.1 SET type is converted into a C or C++ structured type that is identical to that for SEQUENCE as described in the previous section. The only difference between SEQUENCE and SET is that elements may be transmitted in any order in a SET whereas they must be in the defined order in a SEQUENCE. The only impact this has on ASN1C is in the generated decoder for a SET type.

The decoder must take into account the possibility of out-of-order elements. This is handled by using a loop to parse each element in the message. Each time an item is parsed, an internal mask bit within the decoder is set to indicate the element was received. The complete set of received elements is then checked after the loop is completed to verify all required elements were received.