Dynamic allocation provides message text for failed allocation requests. It is usually easier to use this message text rather than decode allocation return codes.

BPXWDYN can return these messages to a REXX program. By default, the messages are returned in the S99MSG. stem. S99MSG.0 contains the number of messages and S99MSG.1 through S99MSG.n contain the message text.

To change the name of the stem, use the MSG key. A stem is not required. Digits are simply appended to the variable specified by the MSG key.

You can also use the MSG key to request allocation to issue the messages to your job log (write to programmer using WTO).

Under z/OS UNIX, you can have messages written to opened files by providing the file descriptor number as the argument to the MSG key. For example, MSG(2) writes messages to the STDERR file.