Thanks for the reply, and I am already familiar with the differences between BY VALUE and BY REFERENCE. In my particular case all CALL parameters are BY REFERENCE (by default, no BY phrases are used), and I expected the nested COMMON subprogram to use the address passed in the call that referred to the structure passed by the outermost program. None of the same-named structures are declared GLOBAL.
But I also expected the compiler to recognize while processing the code in the nested subprogram that references to the same-named structure fields in the nested subprogram were in fact intended to be references to the structure defined in the LINKAGE section of that nested subprogram (i.e., use the "nearest" field definition, not the outermost one), and not direct references to the same-named structure fields defined in the in the outermost program. It was a surprise to me that the compiler did not assume that it should use the LINKAGE section definition In any case, the same storage area is referred to, and changes made by the nested subprograms do indeed change the value as seen in the outermost program, and that was the intended result. Peter -----Original Message----- From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Jon Butler Sent: Thursday, October 14, 2021 8:12 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: COBOL 6.2 - use of identical data name in a nested COMMON subprogram generates a IGYPS0037-S compiler error The Linkage Section is how modules pass data from the top module in the chain down, and then back. In fact, they don't "pass" the data at all, but use a single address that is established by the top-most caller. All modules use the same address which is located in the top-most module's DSECT, irrespective of the variable's name...although in your case the name is the same in both caller and called module. This is how external CALLs work. As you note, INTERNAL calls establish a new variable unless the GLOBAL attribute is applied. Why the compiler was built that way is an interesting question perhaps Tom Ross can answer. Remember, internal subroutines are relatively new in COBOL, but even so, you are asking the question some 20 years too late. BY CONTENT may be what you want in the CALL statement. You can override the standard behaviour ( BY REFERENCE) by using BY CONTENT, where the called module can change the value locally, but not affect the caller; or by using BY VALUE (not recommended by me) where the value is passed and the called module can change the format as long as it's commensurate, e.g. Binary to Fixed Decimal or Float (comp-2). You can mix CONTENT, REFERENCE and VALUE in the same call for different variables. <Code samples snipped> -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
