Boolean types in Delphi

Four Boolean types are defined in Delphi: Boolean, ByteBool, WordBool, and LongBool. The last three Boolean types are introduced for compatibility with other languages. In general, the Boolean type is recommended.

The amount of memory occupies these four types of boolean values ​​is as follows:

Boolean 1 Byte

ByteBool 1 Byte

WordBool 2 Bytes (1 Word)

LongBool 4 Bytes (2 Words)

For ByteBool, the values ​​of the three types of True constants, WordBool and LongBool, are non-zero, and False is zero, which can be verified by the Ord function;

For Boolean type, the value of True constant is 1 and False is zero. In the context of expecting Boolean values, the compiler converts non-zero values ​​of ByteBool, WordBool and LongBool to True.

However, boolean expressions and Integer/Real are incompatible in Delphi. The following table compares the similarities and differences between Boolean and ByteBool/WordBool/LongBool:

Boolean

False < True

Ord(False) = 0

Ord(True) = 1

Succ(False) = True

PRed(True) = False

BoolToStr(True) = -1 //This function is very abnormal

BoolToStr(False) = 0

ByteBool, WordBool, LongBool

False <> True

Ord(False) = 0

Ord(True) <> 0

Succ(False) = True

Pred(False) = True

The BoolToStr function is the most inexplicable. It clearly says that the value of True is 1, but it tells us that True is -1. The prototype of the function is:

function BoolToStr(B: Boolean; UseBoolStrs: Boolean = False): string;

The following table is the conversion rules for functions:

BUseBoolStrsValue of returned string

TrueFalse'-1'

True True The first value of TrueBoolStrs array (default, 'TRUE')

False False '0'

False True The first value of the FalseBoolStrs array (default, 'FALSE')