FORTRAN, Statements, STRUCTURE
*Conan The Librarian
Indicates the beginning of the record structure declaration and defines the name of the structure. Declaration format: STRUCTURE [/str/][fnlist] fdcl [fdcl] ... [fdcl] END STRUCTURE str Identifies a structure name, which is used in subsequent RECORD statements to refer to the structure. A structure name is enclosed in slashes. fnlist Identifies field names when used in a substructure declaration.(Only allowed in nested structure declarations.) fdcl (Also called the declaration body.) Is any declaration or combination of declarations of substructures, unions, or typed data, or PARAMETER statements. Subsequent RECORD statements use the structure name to refer to the structure. A structure name must be unique among structure names, but structures can share names with variables (scalar or array), record fields, PARAMETER constants, and common blocks. Structure declarations can be nested (contain one or more other structure declarations). A structure name is required for the structured declaration at the outermost level of nesting, and optional for the other declarations nested in it. However, if you wish to reference a nested structure in a RECORD statement in your program, it must have a name. Structure, field, and record names are all local to the defining program unit. When records are passed as arguments, the fields must match in type, order, and dimension. Unlike type declaration statements, structure declarations do not create variables. Structured variables (records) are created when you use a RECORD statement containing the name of a previously declared structure. The RECORD statement can be considered as a kind of type declaration statement. The difference is that aggregate items, not single items, are being defined. Within a structure declaration, the ordering of both the statements and the field names within the statements is important because this ordering determines the order of the fields in records. In a structure declaration, each field offset is the sum of the lengths of the previous fields. The length of the structure, therefore, is the sum of the lengths of its fields. The structure is packed; you must explicitly provide any alignment that is needed by including, for example, unnamed fields of the appropriate length. By default, fields are aligned on natural boundaries; misaligned fields are padded as necessary. To avoid padding of records, you should lay out structures so that all fields are naturally aligned. To pack fields on arbitrary byte boundaries, you must specify a compiler option. You can also specify alignment for fields by using the cDEC$ OPTIONS general directive. In the following example, the declaration defines a structure named DATE. This structure contains three scalar fields: DAY (LOGICAL*1), MONTH (LOGICAL*1), and YEAR (INTEGER*2). STRUCTURE /DATE/ LOGICAL*1 DAY, MONTH INTEGER*2 YEAR END STRUCTURE See also COMPATIBILITY_FEATURES RECORD_STRUCTURE in this Help file.
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