Designating the Host File System

Each time the COBOL application creates a new file, it needs to know which file system to use. The run-time checks the file system to use when the file is opened. You provide the name of the file system with one of two run-time configuration file variables. The first is:

DEFAULT_HOST filesystem

This will designate the file system to be used for newly created files that are not individually assigned. For example,

DEFAULT_HOST ODBC

means that all new files will be ODBC files unless otherwise specified by the second configuration variable, which is:

filename_HOST filesystem

where filename is the file name, without any extension, named in the ASSIGN TO clause of your SELECT statement. This configuration variable is used to assign an individual data file to a different file system. Any file so assigned will use the designated file system, and not the one specified by DEFAULT_HOST. For example,

myfile_HOST VISION

means that myfile will be under the Vision file system. The ability to designate a different file system for certain files enables you to tailor your application to a specific customer’s needs or to implement an incremental conversion for a customer. With relational databases, this is particularly useful in that it allows you to tune an application for processing speed and resource requirements.

You can use these run-time configuration file variables in combination to assign your new files in a default with exceptions manner; for example, this set of entries:

DEFAULT_HOST VISION
afile_HOST ODBC
bfile_HOST ODBC

means that all new files except afile and bfile will be assigned to Vision, and those two files will be assigned to ODBC.

You can also change the values of these variables during program execution by including in your code:

SET ENVIRONMENT "filename_HOST" TO filesystem

or

SET ENVIRONMENT "DEFAULT_HOST" TO filesystem

This enables you to change file systems during the execution of your program. This is not the typical way to specify a file system; normally it is designated in the run-time configuration file and is not changed in the COBOL program.