Implementation of Sequences and Sets

The concepts of ASN.1 sequences-of and sets-of are not inherent in C. Arrays are adequate for static usage. Dynamic usage is often implemented through the usage of linked lists. For implementation purposes set-of and sequence-of are considered the same. Relevance of order is the user's view and not an implementation issue. Only the implementation of sequence-of is described here.

ASN.1 sequence concept maps to struct in C. With this understanding, for design purposes a shorthand notation is adapted to make the concept of sequence-of more natural to C. The following keyword extension are made:

        sequence
        sequenceof

Their usage is similar to struct and union. sequence specifies an element of a list. sequenceof specifies the head of a list. These are based on the QU_ and SEQ_ module. sequence and sequenceof can be used for data or instance declaration.

Consider the following example:

        typedef sequence SomeInfo {
                Int someField;
        } SomeInfo;

Which is equivalent to:

        typedef struct SomeInfo {
                struct SomeInfo *next;
                struct SomeInfo *prev;
                Int someField;
        } SomeInfo;

For a sequenceof instance declaration, consider:

        sequenceof SomeInfo someInfoSeq;

Which is equivalent to:

        struct {
                SomeInfo *first;
                SomeInfo *last;
        } someInfoSeq;

For a sequenceof type declaration, consider:

        typedef sequenceof SomeInfo {
                Int nuOfElems;
        } SomeInfoSeq;
        SomeInfoSeq someInfoSeq;

Which is equivalent to:

        typedef struct {
                SomeInfo *first;
                SomeInfo *last;
                Int nuOfElems;
        } SomeInfoSeq;
        SomeInfoSeq someInfoSeq;

Implementation of sets-of can be done as sequences-of. The user may convey the irrelevance of order through the usage of:

        set
        setof

reserved word extensions.