The format of the name of each generated 3GPP layer 3 encode function is as follows:

   x3GL3Enc_[<prefix>]<prodName>

where <prodName> is the name of the ASN.1 production for which the function is being generated and <prefix> is an optional prefix that can be set via a configuration file setting. The configuration setting used to set the prefix is the <typePrefix> element. This element specifies a prefix that will be applied to all generated typedef names and function names for the production.

It is also possible to change the 'x3GL3' prefix at the beginning of the function name by using the <protocol> configuration setting. For example, an API was generated for the Non-Access Stratum (NAS) protocol within the ASN1C package. A protocol setting of NAS was used for this, so all encode function names begin with 'NASEnc_' instead of 'x3GL3Enc_'.

The calling sequence for each encode function is as follows:

   status = x3GL3Enc_<name> (OSCTXT* pctxt, <name>[*] value);

In this definition, <name> denotes the prefixed production name defined above.

The pctxt argument is used to hold a context pointer to keep track of encode parameters. This is a basic "handle" variable that is used to make the function reentrant so it can be used in an asynchronous or threaded application. The user is required to supply a pointer to a variable of this type declared somewhere in his or her program.

The value argument contains the value to be encoded or holds a pointer to the value to be encoded. This variable is of the type generated from the ASN.1 production. The object is passed by value if it is a primitive ASN.1 data type such as BOOLEAN, INTEGER, ENUMERATED, etc.. It is passed using a pointer reference if it is a structured ASN.1 type value. Check the generated function prototype in the header file to determine how the value argument is to be passed for a given function.

The function result variable stat returns the status of the encode operation. Status code 0 (0) indicates the function was successful. Note that this return value differs from that of BER encode functions in that the encoded length of the message component is not returned – only an OK status indicating encoding was successful. A negative value indicates encoding failed. Return status values are defined in the "asn1type.h" include file. The error text and a stack trace can be displayed using the rtxErrPrint function.

It is possible to add extra arguments to 3GPP Layer 3 encode functions through the use of the <addarg> configuration setting. This is normally done to pass data from container type member variables into an encode function.