The following rules apply to COBOL user exits. Failure to observe these COBOL user exit rules can result in termination or unpredictable results.

• User exits written in COBOL must not use STOP RUN statements. To return to DFSORT, use the GOBACK statement.
• VS COBOL II user exits must be compiled with the RES and RENT compiler options.
• If a user exit contains a DISPLAY statement, the DFSORT messages normally written to SYSOUT must be directed to another data set using the MSGDDN parameter. For DISPLAY statements, COBOL also writes to SYSOUT. The messages to SYSOUT can, therefore, be lost because of interleaving of output.

  An alternative is to direct the COBOL output to another data set by using the OUTDD compiler option.

• COBOL user exits must not contain a SORT or a MERGE verb.
• When coding the MODS control statement to describe a COBOL user exit, use C for the fourth parameter. This instructs DFSORT to build the correct parameter list.
• If invoking DFSORT from a COBOL program, you can use a COBOL E15 if the FASTSRT option is in effect for input and a COBOL E35 if FASTSRT is in effect for output.
• COBOL library routines in Language Environment must be available at run time.