In a message dated 4/24/2006 1:41:01 P.M. Central Daylight Time, [EMAIL PROTECTED] writes:
>I've got a program that opens a VB PDS (RECFM=VB,BLKSIZE=2550,LRECL=255). >But - note that I said it opens the PDS, not a member of the PDS. That >open succeeds, and presumably, the program will merrily try to >read the PDS directory as Format-V records. >So - the first read succeeds, and it gets these bytes back for >the first 6: > 000EFFFF FFFF > | BDW | | RDW .... The first block in a PDS is the first block of the directory, which has a fixed format (lrecl=blksize=256 with 8-byte keys). Presumably your program is not trying to do a Read Key and Data but rather a Read Data CCW, so you do not read the key but instead read only the first data block in the directory. The first 2 bytes in the data area of a PDS directory block are the number of bytes in that 256-byte block that are used. You show 000E. I did an IMASPZAP dump of a CNTL PDS of mine and found two blocks with 00FE in the first two bytes, and the third block had X'000EFFFFFFFFFFFFFFFF00000000' at the beginning. The 8 bytes of FF are a fake member name of all X'FF' so that it will always be last when all the member names are sorted into ascending sequence. A PDS directory is supposed to have its member names in that sequence. In my case, the 000E is the correct number of bytes used in this block, as the minimum length of one entry is 8 for the member name, 3 more for the relative TTR within the PDS where the member begins, and 1 byte of flags. The minimum entry length is then 12. Two more bytes for the obligatory 2-byte block length at the beginning yields 14 bytes. A block that begins as this one does is a block indicating the last directory block with any meaningful information in it, and in this case the meaningful info is the fake member name showing the end of the directory's list of members. There are more blocks in my directory after this one, and they are all X'00'. It looks as if your PDS is completely empty. That would explain why you see 000EFFFFFFFF in the first 6 bytes. The read CCW does not move any bytes around, change them, or interpret them. It reads what is on the track. Then the VBS access method will assume that the first 2 bytes are the block length, then 2 reserved bytes, then 2 RDW bytes, etc. In other words, because you told QSAM to read a PDS directory block and to treat it as VBS data, you have thoroughly confused not only the access method but also yourself. You need to put a lot more logic into your program; i.e., be sensitive to file organization type (DSORG=PO for a PDS), etc. I cannot begin to suggest what extra logic you should add, since I do not know the purpose of your program or why you want to read a PDS with it including its directory. A much better way to read through a PDS is with BSAM, which can also read through any other data set organization. But you have to code more logic after each block is read in with the READ/CHECK macros. >what's a program "to do" with what the user types. I cannot understand the meaning of this phrase. >Should it look at the lrecl/blksize in the DCB and decide that >this doesn't make sense? What if it did make sense - then what? At the very least, your program must look at the data set organization. "Then what" depends on what you want your program to do, which I don't know. >Or - is there a way to know this is a bunch of bytes from a >PDS directory... and this READ doesn't make sense? Your program can know that this bunch of bytes is a PDS directory because it is the first block in the input data of a PDS. The end of the directory is marked by an end of file record. That will probably confuse your program, too. Then the first block of the first member begins after the end of file record, unless the first member has been deleted after the second member was added, in which case what you will read next is what used to be the first member, which also ends with another end of file record. More confusion. I would suggest a complete redesign of your program beginning with a thorough understand of what your program is supposed to accomplish, followed by research into the internals of a PDS. Bill Fairchild ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
