dctx

A decode context created by mtaMessageDecode().

item

Item identifier specifying which string-value item to return. See the description that follows for the list of permitted values for this argument. 

str

An optional pointer to receive the address of the requested string. The string will be NULL terminated. A value of NULL may be passed for this argument. 

len

An optional pointer to receive the length of the requested string. This length is measured in bytes and does not include the NULL terminator at the end of the string. A value of NULL may be passed for this argument.