How do I select a CHOICE component?

The following example and also exists as a part of a sample in the sample directory. Shown first is field of a SEQUENCE in the ASN.1 definition.

operation [7] CHOICE
        createReqt [0] CreateReqt,
        updateReqt [1] UpdateReqt

The representation of a CHOICE type is a structure which includes a choice field and element fields (for each CHOICE alternative). In addition to these fields, #define constants are also defined for each alternative in the CHOICE type. For the ASN.1 above, the following is generated.

struct {
  unsigned short choice;
     # define createReqt_chosen 1
     # define updateReqt_chosen 2
        union {
        CreateReqt createReqt; /* to choose, set choice to
                * createReqt_chosen */
                UpdateReqt updateReqt; /* to choose, set choice to
                * updateReqt_chosen */
                } u;
                } operation;

To specify that a particular alternative is selected, all you have to do is set the choice field equal to the #define constant that corresponds to the selected alternative.

myMsg.operation.choice = createReqt_chosen;
      myMsg.operation.u.createReqt.ordId = 5432;
      actionOctStr, 5); 

myMsg.operation.u.createReqt.action.length = 5;
       memcpy(myMsg.operation.u.createReqt.fldNm.value, fldNmOctStr,          15);

myMsg.operation.u.createReqt.fldNm.length = 15;
        myMsg.operation.u.createReqt.creditChecked = TRUE; 

For the complete example (including the definition of createReqt), refer to the ASN.1/C Runtime Functions Reference section.


The samples included with some of the Knowledge Center answers are meant for your general understanding of the OSS products. Different versions of the products might produce slightly different outputs. Consult the products documentation and samples for the most up-to-date products information and code examples.

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