How to read a PS file in reverse order?

I have a PS file to be read in reverse order and process accordingly. Do we have a way to mention to read the file in reverse order in FD in COBOL module? OR do we have something to achieve the same using SORT?

Note: Reading the records into a buffer (array) and using it in reverse order would be the first idea that 开发者_如何学Pythoncomes to mind but that way doesnt work for file with millions of records.

Your suggestions will be appreciated.

I do not believe there is a standard method for doing this in COBOL. However, if the file contains fixed length records you might try processing it as a relative file and just run thourgh it by descending record number. The other option is, as you suggest, sort it in reverse order then process as "normal".

If the device the file is on supports it, you can use "OPEN INPUT fname REVERSED". But the file will need to be on a tape or a device that is pretending to ba a tape.

Some versions of COBOL support a READ LAST statement to get the last record on the file. Then use READ PRIOR to read the file in reverse order. Not sure what COBOL version you're working with.