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This command-line compiler option enables/disables checking for undefined values.

Syntax: -u[+|-]

Default: Enabled

Notes: When this option is enabled the compiler generates code which checks each time your program gets a value from a variable to make sure that the value is not undefined. If your program does get an undefined value from a variable then the code generated by the compiler will issue a run-time error message and terminate your program.

So for example if you compile and run the following program

   program bad(output);
   var
      r : real;
   begin
      writeln(r) (* The value of "r" is undefined *)
   end.

The program will terminate with a run-time error message because of the attempt to print the value of r which is undefined. Unfortunately not all variable accesses can be checked, checks are only made for accesses to variables of the following types:

• enumerated types (including boolean)
• subranges of enumerated types
• subranges of integer that do not include -1
• file
• list
• object
• pointer
• real
• set (array representation)

Checking for undefined values is performed as follows:

• All memory is initialized by setting all bits to 1.
• When accessing a variable a check is performed to see if all bits are set and if they are this variable is undefined. This doesn't work for char, integer or set (bit set representation) variables since a value with all bits set to 1 is valid for these variables. Record variables are not checked because they may contain fields which can not be checked.

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