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 binary 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 binary 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 binary object and append the PDU parts to it. Other classes also provide a serialize() member, e.g. the OidValue and IntegerValue classes. PDU's typically call the serialize() functions of the contained objects, receive a binary object from that object and append it to their own binary 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 binary object, named 'serialized':

binary 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 OidValue object. The OidValue 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 OctetStringValue object. Again, the OctetStringValue 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;