Tapes

z/OS® XL C/C++ supports standard label (SL) tapes. If you are creating tape files, you can only open them by ddname. z/OS XL C/C++ provides support for opening tapes in read, write, or append mode, but not update. When you open a tape for read or append, any data set control block (DCB) characteristics you specify must match those of the existing data set exactly. The repositioning functions are available only when you have opened a tape for read. For tapes opened for write or append, calling rewind() has no effect; calls to any of the other repositioning functions fail. To open a tape file for write, you must open it by ddname.

Opening FBS-format tape files with append-only mode is not supported.

When you open a tape file for output, the data set name you specify in the JCL must match the data set name specified in the tape label, even if the existing tape file is empty. If this is not the case, you must either change the JCL to specify the correct data set name or write to another tape file, or reinitialize the tape to remove the tape label and the data. You can use IEBGENER with the following JCL to create an empty tape file before passing it to the subsequent steps:

//ALLOC EXEC PGM=IEBGENER
//SYSUT1 DD *
/*
//SYSUT2 DD DSN=name-of-OUTPUT-tape-file,UNIT=xxxx,LABEL=(x,SL),
//       DISP=(NEW,PASS),(DCB=LRECL=xx,BLKSIZE=xx,RECFM=xx),
//       VOL=SER=xxx
//SYSIN DD DUMMY
//SYSPRINT DD SYSOUT=*

Note: For tapes, the value for UNIT= can be TAPE or CART.

Because the C library does not create tape files, you can append only to a tape file that already exists. Attempting to append to a file that does not already exist on a tape will cause an error. You can create an empty data set on a tape by using the utility IEBGENER.