RPG IV Warning! Check %ERROR or %STATUS before other I/O BIFs

Here's an important piece of advice for RPG IV database programming. When you use RPG IV built-in functions (BIFs) to check the result of an I/O operation, be sure you check the %Error or %Status BIF first. If %Error is true ('1'), the value of the %Found, %Equal, and %Eof BIFs should be ignored. For example, if you attempt to read a record that's locked by another job, %Error returns true, but %Found returns false ('0'). Here's an example of properly sequenced tests:

*...1....+....2....+....3....+....4....+....5....+....6....+....
C     SlcKey        Chain (E) Master
C                   Select
C                     When    %Error
C                       ExSr  MasterIOErr
C                     When    Not %Found( Master )
C                       ExSr  MasterNFnd
C                     Other
C                       ExSr  ProcMaster
C                   EndSl

Here's a different approach using the %Status BIF:

*...1....+....2....+....3....+....4....+....5....+....6....+....
D FStsOK          C                   Const(  0 )
D FStsNoKey       C                   Const( 12 )
  .
  .
  .
C     SlcKey        Chain (E) Master
C                   Select
C                     When    %Status( Master ) = FStsOK
C                       ExSr  ProcMaster
C                     When    %Status( Master ) = FStsNoKey
C                       ExSr  MasterNFnd
C                     Other
C                       ExSr  MasterIOErr
C                   EndSl 

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