In COBOL, a copybook is a separate and reusable file that contains data items and record declarations, along with other common elements used in multiple COBOL programs. The copybook serves as a template or blueprint for defining data structures that are shared across various COBOL programs.
Instead of duplicating the same data declarations in multiple programs, the copybook allows programmers to centralize the data definitions in one place. Programs can include the content of the copybook using the "COPY" statement during the compilation process. The "COPY" statement inserts the copybook's content directly into the source code of the program, as if the data declarations were part of the program itself.
The benefits of using copybooks are the following:
Reusability: By defining data structures once in the copybook, they can be shared among different programs, reducing redundancy and ensuring consistency.
Maintenance: Any updates or modifications to the data structures can be made in the copybook, and those changes will be automatically reflected in all programs that include it.
Readability: Separating data declarations into a copybook makes the main program's source code more concise and easier to read.
Modularization: Copybooks promote modular programming by encapsulating data definitions, making it easier to manage and understand large programs.
Copybooks typically have a ".cpy" file extension and contain data item declarations, record layouts, and sometimes other COBOL statements. However, they do not contain program logic or procedure divisions, focusing solely on providing reusable data structures for multiple programs.
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