ERangeError Class

ERangeError is the exception for Delphi range errors.

Pascal

ERangeError = class(EIntError);

C++

class ERangeError : public EIntError;

File

SysUtils

Description

ERangeError occurs in Delphi code when range checking is enabled and an ordinal values goes outside its declared range.

Note: Range checking is not a C++ feature. However, ERangeError can occur when C++ code calls Delphi code.

Note: By default, the Delphi compiler disables range checking. The compiler can always detect obvious range errors, which prevents the following code from compiling.

//Delphi subrange example

Copy Code

var
  SmallValue: 1..3;
  SevenBits: byte;
begin;
  SmallValue := 4;  //Won't compile: constant expression out of bounds
  SevenBits := 256; //Won't compile: constant expression out of bounds

end;

Note: However, the compiler can't anticipate out-of-range values provided at run time:

//Delphi subrange example

Copy Code

var
  SmallValue: 1..3;
  SevenBits: byte;
  ThirtyTwoBits: Integer
begin;
  ThirtyTwoBits := 4;
  SmallValue := ThirtyTwoBits; //Assigns 4 to SmallValue (SmallValue is stored as a Byte)
  ThirtyTwoBits := 256;
  SevenBits := ThirtyTwoBits;  //Assigns 0 to ThirtyTwoBits (high-order bits discarded)

end;

Note: If range checking is enabled, both out-of-bounds assignments throw ERangeError exceptions. To enable range checking, use the Project option in the IDE or the $R+ directive.

Note: Range checking is considered a debugging feature. It produces bigger and slower executables.

Note: Do not confuse ERangeError with ERangeException, which relates to errors using graduated controls in VisualCLX.