A file constant is an identifier declared with the FILE attribute and without the VARIABLE attribute. For example:
DECLARE F FILE;
In this example, F is the name of a file constant.
A file constant cannot be the target of an assignment operation, and is external, by default. (For a discussion of assignment statements, see the chapter Statements.)
Each file constant is associated with a block of static storage called a file control block. The file control block retains information about the current status of the file while the file is open. In effect, the file constant is a pointer to, or a designator of, a file control block. File constants require the use of the -defext compiler option.
Each file control block's file identifier (ID) is the NAME of its associated file constant. The file ID in the previous example is F. This ID is used as the default TITLE of the file when it is being opened.