Structure Variables

A structure variable can be used in two different ways if your Fortran compiler supports structures. First, the structure can be used as a simple variable, implying that all its members are used. This would be appropriate in the Embedded SQL select, fetch, and insert statements. Second, a member of a structure may be used to refer to a single element. This member must be a scalar value (integer, real or character string).

The syntax for referring to a complete structure is the same as referring to a simple variable:

• The structurename can refer to a main or nested structure. It can be an element of an array of structures. Any variable reference that denotes a structure is acceptable. For example:

C A simple structure
        :emprec
C An element of an array of structures
        :struct_array(i)
C A nested structure at level 3
        :struct.minor2.minor3

• In order to be used as a collection of variables, the final structure in
the reference must have no nested structures or arrays. All the members of the structure will be enumerated by the preprocessor and must have scalar values. The preprocessor generates code as though the program had listed each structure member in the order in which it was declared.

• You must not use a structure containing a union declaration when the structure is being used as a collection of variables. The preprocessor generates references to all components of the structure and ignores the map groupings. Using a union declaration results in either a "wrong number of errors" preprocessor error or a runtime error.

The following example uses the" employee.dcl" file that DCLGEN generates to retrieve values into a structure. This example is not applicable if DCLGEN was run with the -f77 flag:

    exec sql begin declare section
             exec sql include 'employee.dcl'
    exec sql end declare section
    exec sql select *
1    into :emprec
2    from employee
3    where eno = 123

The example above generates code as though the following statement had been issued instead:

exec sql select *
1   into :emprec.eno, :emprec.ename, :emprec.age,
2       :emprec.job, :emprec.sal, :emprec.dept
3   from employee
4   where eno = 123

The example below fetches the values associated with all the columns of a cursor into a record:

exec sql begin declare section
            exec sql include 'employee.dcl'
exec sql end declare section

exec sql declare empcsr cursor for
1   select *
2   from employee
3   order by ename
             ...

exec sql open empcsr
        exec sql fetch empcsr into :emprec
exec sql close empcsr

The following example inserts values by looping through a locally declared array of structures whose elements have been initialized:

exec sql begin declare section
         exec sql declare person table
         1    (pname     char(30),
         2     page      integer1,
         3     paddr     varchar(50)

         structure /person_/
                    character*30  name
                    integer*2     age
                    character*50  addr
         end structure
         record /person_/ person(10)
         integer*2 I

exec sql end declare section
            ...

do i=1,10
            exec sql insert into person
            1   values (:person(i))
end do

The insert statement in the example above generates code as though the following statement had been issued instead:

exec sql insert into person
1 values (:person(i).name, :person(i).age,:person(i).addr)

The syntax Embedded SQL uses to refer to a structure member is the same as in Fortran:

• The structure member denoted by the above reference must be a scalar value (integer, real or character string). There can be any combination of arrays and structures, but the last object referenced must be a scalar value. Thus, the following references are all legal:

C Member of a structure
       :employee.sal
C Member of an element of an array
       :person(3).name
C Deeply nested member
       :struct1.mem2.mem3.age

• Any array elements referred to within the structure reference, and not at the very end of the reference, are not checked by the preprocessor. Consequently, both of the following references are accepted, even though one must be wrong, depending on whether "person" is an array:

• The preprocessor expects unambiguous and fully qualified structure member references.

The following example uses the "emprec" structure, similar to the structure generated by DCLGEN, to put values into the "empform" form.

Example: Structure member usage

        exec sql begin declare section
                    structure /emprec_/
                        integer*2       eno
                        character*2     ename
                        integer*2       age
                        integer*2       job
                        real*8          sal
                        integer*2       dept
                    end structure
    record /emprec_/ emprec

exec sql end declare section
    ...

exec frs putform empform
1    (eno = :emprec.eno, ename = :emprec.ename,
2     age = :emprec.age, job = :emprec.job,
3     sal = :emprec.sal, dept = :emprec.dept)