Accessing COBOL Data Groups
Several examples of how to utilize COBOL in a Microsoft .NET environment have been circulating for a number of years. Some of these examples are quite dated and due to Framework enhancements, (2.0, 3.0, 4.0, 4.5 and now 4.6) the use of the namespaces as well as the syntax used to access them has changed significantly. Micro Focus recently released Visual COBOL 2.3, our flag-ship product for Visual Studio 2015. With a number of changes that have occurred in both .NET and Visual COBOL an update of all our previous articles is in order. So over the next couple of months we will be updating all of our previous articles to the latest versions and introducing new articles with new content. We hope you find these articles educational and valuable to you and a benefit to your organization.
This particular article has benefited from a number of changes in Micro Focus Visual COBOL. The addition of interfacing capabilities in .NET and JVM have made the process of accessing data hidden in COBOL applications much simpler for not only the C# developer but also for the COBOL developer who has to provide the access to the data stores. Spend a few minutes reviewing the article and see how simply you can now access COBOL based data from C# or VB.NET or Java or any other distributed language.
COBOL programmers have for years used '01' level (or Group Descriptions) as a means of creating a data structure for related items. It would be safe to say these Data Groups are used in just about every COBOL program that has been written and probably will ever be written. They provide a quick way for COBOL programmers to group together data that has some form of relationship. For example, the name of a region and the total sales for a particular timeframe as in the following structure:
In the above sample we see an '01' (or Group) description for a field called WS-Branch-Rec. This is the highest definition for a related group of data items. Underneath this item there are two additional data items, WS-BRANCH-NAME and WS-BRANCH-TOT. Each of these items occurs 10 times in a table. You can think of the structure in terms of a spreadsheet, 10 rows with two columns of data. The variable WS-BRANCH-NAME is defined as a "PIC X(50)" which means it is 50 characters in length and is an alphanumeric data item (or a String in C#). WS-BRANCH-TOT is defined as a "PIC 9(12)" is a numeric data item. The equivalent in C# would be an integer.
In this article we will begin with a C# console application calling a COBOL DLL file. The C# application will pass it a number of occurrences to create a table (much like a user requesting a specific number of months to report on). The COBOL program will accept the user request (which we have currently defaulted to 5), create the data group and pass control back to the C# program. The C# program will then read in the data group and display the results on the screen.
Please keep in mind that while the example is not of a completely finished and polished application the intent is to demonstrate how to utilize your existing COBOL business logic and interact with a new C# front-end.
We will assume you are comfortable with the C# language. If you have any questions in this area please consult with one of your local C# experts.
As we mentioned above, we will call the COBOL program, passing it a variable to define the number of occurrences we wish to populate. The following code illustrates how to do this:
The first three lines are basic display statements to inform the operator we are beginning the process. The fourth line of code though instantiates our COBOL program. The fifth line of code is the key to working with the COBOL data groups. In this line we create an instance of the data that we have defined in our COBOL program. This data has been exposed using a compiler directive added when the COBOL program was built within Visual Studio.
In the Properties for the COBOL program we added two new compiler directives: ilsmartlinkage and ilcutprefix(WS-) as shown:
The two compiler directives:
Exposes the linkage section and entry points to managed code by creating types
Removes a specified prefix from the names of the COBOL data items in the source code
The COBOL program has had no changes made to it. It was simply recompiled with the above two directives to expose the linkage section for use by other languages.
The PERFORM loop creates the number of occurrences in the table based on the input parameter CTR. This parameter was passed to it by the C# class. This is standard COBOL and we will not delve into an explanation of this code other than to mention this could be your existing COBOL program(s). They would continue to operate and perform the tasks for which they were designed.
Returning to the C# program
Upon our return to the C# program we need to retrieve the data. The following code accomplishes this and displays it to the console window:
We have created a 'for loop' to process the correct number of times according to our previously defined counter (Ctr). Again, one note, the .NET Framework operates as zero based, not one based so we need to begin our array index at zero. This implies then that our ending number will be one less than the count the COBOL system utilized, or 4 in our case. The 'for loop' has been created to begin at zero, determine if "ctr" is less than or equal to 4 and then increment the counter if it is.
Within the 'for loop' the first line of code retrieves the amount using a ‘get’ method for the data item which was created as part of the compilation process by the COBOL compiler. A similar statement is executed for the ‘name’ data element and written out to the console. When processing has completed a ‘readline’ is executed so you can see the data before the window closes.
The ZIP file has all the necessary source code for you to follow along and see how the code is to be structured. Being able to utilize an existing COBOL data structure in the .NET Framework will greatly expand the interoperability and life of your existing COBOL applications but also provide .NET Developers a way to access data that is much simpler and straightforward. While the process may seem complicated at first, spend a few minutes and analyze what we've done in this article. The steps will be basically the same for you and will greatly extend the usefulness of your existing applications to the .NET Framework. And that's what it's all about...
An Eclipse version of the Data Groups project is attached as well. The same principles apply showing how Java can interact with COBOL data.