Association is the pathway along which entities in the same or different scopes communicate. Scope specifies the part of a program where an entity is known and accessible. Thus, the three topics - scope, association, and definition - are related. In certain cases, such as for the integer object in the preceding example, certain values are considered to be undefined references to undefined values do not conform to the standard. This meaningless value is called an undefined value. For example, if a real object is equivalenced (storage associated) with an integer object, defining the real object with a valid real value causes the integer object to acquire a meaningless value. In some cases, such associated object values can be unpredictable or unreliable. For example, assignment statements and input statements define objects directly by name, which can also cause associated items to become defined. The association methods were introduced in previous sections and include association through arguments (argument association), association through storage (storage association), association through modules (use association), association through hosts (host association), and association through name aliases (pointer association).Īfter objects are associated, there can be multiple ways to define values for them. To both communicate data between program units and limit and control accessibility of data, the language defines the concept of association, which relates local objects within and between program units. The spectrum of scope varies from an entire program (global), to individual program units (local), to construct definitions, to statements or parts of statements. Scope specifies that part of a program in which a particular entity is known and accessible.
The concept of scope is introduced in the Fortran Language Reference Manual, Volume 1. However, there are some situations in which it is necessary to know all the details, particularly when modifying or maintaining programs, or looking for subtle bugs. If simple programming disciplines are followed, many of the subtle issues and concerns related to scope, association, and definition can be avoided in writing correct programs. Fortunately, all of the detailed rules and conditions presented in this chapter usually are not necessary in order to construct pieces of Fortran programs. These topics were not presented completely in previous chapters because a comprehensive and thorough understanding of the entire language is needed to fully assimilate these topics. Scope, association, and definition (value assignment) provide the communication pathways between the different parts of the program.
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