The compiler option INITAUTO will add an appropriate INITIAL attribute to any AUTOMATIC variable that does not have an INITIAL attribute if the variable has one of the attributes
See the Programming Guide for more details.
The compiler option DFT(INITFILL) will fill all AUTOMATIC storage will a specified byte value (or to '00'x if no byte value is specified). This can be used to initialize variables with these attributes
The compiler option INITFILL will also fill all other AUTOMATIC variables with the specified (or default) byte value, but these variables would not really be properly initialized. For example, use of a FIXED DEC variable initialized via DFT(INITFILL) will lead immediately to a data exception.
Setting the third suboption of the runtime option to 00 (as in STORAGE(,,00)) will fill all AUTOMATIC storage in all the routines (including library routines) with the hex value 00. This has the same effects and validity as the DFT(INITFILL) compiler option except that it applies to all routines in the application and has a dreadfully bad impact on performance. Furthermore, since the compiler does not know if this option is being used, it may not have the desired effect for code compiled with OPT(2) or OPT(3): the fact that a variable is uninitialized makes the code invalid and may lead the optimizer to make choices about how to optimize the code that cannot be repaired by using this runtime option.
Setting the third suboption of the runtime option to CLEAR (as in STORAGE(,,CLEAR)) will fill all AUTOMATIC storage with the hex value 00 before MAIN is invoked. This has the same effects and validity as the DFT(INITFILL) compiler option except that it applies only to the MAIN routine. Furthermore, since the compiler does not know if this option is being used, it may not have the desired effect for code compiled with OPT(2) or OPT(3): the fact that a variable is uninitialized makes the code invalid and may lead the optimizer to make choices about how to optimize the code that cannot be repaired by using this runtime option.