Before sending a PDU to the master agent, it must be serialized to a binary form, which is specified in RFC 2741.

AgentXcpp defines some data types and helper functions to deal with serialization. The type data_t can be used like an STL string, but is a series of byte_t values. The byte_t type in turn is defined to hold a single byte. The write32() and write16() functions are used to append a 32-bit value respectively a 16-bit-value to a data_t object, using big endian. The agentXcpp library always uses big endian (this may change in future).

Each PDU has a serialize() member function to get the serialized form of that PDU. In addition, the PDU class (which is the base class of all concrete PDU classes) provides the add_header() member to add the serialized form of the PDU header. The serialize() functions start with an empty data_t object and append the PDU parts to it. Other classes also provide a serialize() member, e.g. the oid and Integer classes. PDU's typically call the serialize() functions of the contained objects, receive a data_t object from that object and append it to their own data_t object. Finally, PDU::add_header() is called to add the header.

Let's take an example. When an OpenPDU is serialized, the OpenPDU::serialize() function starts by creating an empty data_t object, named 'serialized':

    data_t serialized;

Then the timeout field and 3 reserved fields are appended like this:

    serialized.push_back(timeout);
    serialized.push_back(0);
    serialized.push_back(0);
    serialized.push_back(0);

Next, the ID field is appended which is an oid object. The oid class provides a serialize() function which is used to serialize the OID object:

    serialized += id.serialize();

Then the description field is added, which is an Octet_String object. Again, the Octet_String class provides a serialize() function:

    serialized += descr.serialize();

Finally, the header is added by calling PDU::add_header(), providing the PDU type (which is encoded into the header) and the serialized object (which is directly manipulated by add_header()):

    add_header(PDU::agentxOpenPDU, serialized);

Now the serialization is complete and the data is given to the caller:

    return serialized;