Caché ObjectScript Reference - InterSystems Documentation

Most magnetic tape programs need not be concerned with $ZB unless they must deal withunusual formats and variable length blocks.To monitor magnetic tape operations, your program can test the appropriate bit of $ZA aftereach read and write.The following code checks both $ZA and $ZB after each magnetic tape read, and sets MTERRwhen either of these variables indicates an error. It also sets $ZTRAP when a magnetic tapeerror occurs.; $$MTIN(mtdev) = the next logical record from magtape; device mtdev.; Also returns za=$ZA and zb=$ZB; On a magtape error, mterr=1 and $$MTIN(mtdev)=""; Expects the caller to have set $ZT to trap other; errors.MTIN(io)NEW rec,curdevSET mterr=0,curdev=$IO,$ZT="MTIERR"USE ioREAD recMTIEXITSET za=$ZA,zb=$ZBUSE curdevQUIT recMTIERRIF $ZERROR["MAGTAPE" {USE curdevZQUIT 1GOTO @$ZTRAP }; Use caller's error trap.ELSE {SET $ZTRAP="",mterr=1,rec=""GOTO MTIEXIT }If a terminator completes a READ, Caché mode returns the terminator as a string in $ZB.If an escape sequence terminates a READ, Caché mode returns the ASCII escape sequenceas a string in $ZB.See Also• READ command• WRITE command• $KEY special variable• $ZA special variable• $ZEOF special variable• I/O Devices and Commands in Caché I/O Device Guide• Terminal I/O in Caché I/O Device Guide$ZBCaché ObjectScript Reference 465