[2. Basics of Delphi grammar] 2 Object Pascal data type

2.Object Pascal data type

Object Pascal Is a strong type of language , Definition of data type 、 There are strict syntax rules for declarations, data assignment and transfer operations .Object Pascal The data types of can be divided into standard data types and advanced data types , It also supports custom types . This section mainly studies standard data types .

Standard data type ：

• Integer integer

• Real floating-point

• Charactor Character

• String String type

• Boolean Boolean type

Advanced data types ：

• Enumerated enum

• Subrange Subboundary type

• Set Collection types

• Array An array type

• Record Record type

• File file type

• Class Class types

• Class Reference Class reference type

• Interface Interface type

• Pointer Pointer types

• Procedural Process type

• Variant Variable type

In data types , integer 、 Character 、 Boolean type 、 Enumerations and subjunctions are called sequential types , Its value is an ordered set , Every possible value depends on the order , That is to say, its value corresponds to an integer .

2.1 Numerical data type

1. Integer types

Object Pascal Integer type in ：

Type the name	The word is long	type	Space
ShortInt	8 Bit signed integer	Short	-128~127
Byte	8 Bit unsigned integer	Byte type	0~255
SmallInt	16 Bit signed integer	Small integer	-32768~32767
Word	16 Bit unsigned integer	Font type	0~65536
Integer	32 Bit signed integer	integer	-2147483648~2147483647
Longword	32 Bit unsigned integer	Long type	0~4294967295
Longint	32 Bit signed integer	Long integer	-2147483648~2147483647
Cardinal	32 Bit unsigned integer	Ordinal type	0~4294967295
Int64	64 Bit signed integer	64 An integer	-2^63~2^63

When using integer type , Try to use Integer and Cardinal data type , Because these two data types can maximize CPU and OS Performance of .

2. Real number type

Object Pascal Real number type in ：

Type the name	The word is long	type	Space	Effective bit
Single	4 Byte float	Single-precision floating-point	±1.5*10^-39 ~ 3.4*10^38	7 or 8
Real	6 Byte float	Real type	±5.0*10^-324 ~ 1.7*10^308	15 or 16
Double	8 Byte float	Double precision floating point	±5.0*10^-324 ~ 1.7*10^308	15 or 16
Extended	10 Byte float	Extended	±3.6*10^-4951 ~ 1.1*10^4932	19 or 20
Currency	64 Bit monetary value	Currency type	-922337203685477.5808 ~922337203685477.5807	19 or 20

stay Object Pascal in ,Real The type and Double Types are completely equivalent ,Extended Type ratio Real Type has higher precision , But the compatibility with other platforms is poor , So try to avoid using Extended type .Currentcy Types are specifically designed to handle monetary values , This type must have at least 4 Valid decimal places .

2.2 Character data type

1. Character type

Character types are data types that store single character data ,Object Pascal Character data types in ：

Type the name	type	Space	Value range
AnsiChar	Ansi Character	1	Expand ANSI Character set
WideChar	Wide character	2	Unicode Character set
Char	Character	1	Expand ANSI Character set

Char The type and AnsiChar Types are completely equivalent ; The most commonly used character type is Char type .

2. String type

String type is the data type that stores string data ,Object Pascal String data type in ：

Type the name	type	Maximum length	Memory space
ShortString	Short string	255	2 ~ 256B
AnsiString	Long string	2^31	4B ~ 2GB
WideString	Wide string	2^30	4B ~ 2GB
String	String type	2^31	4B ~ 2GB

• ShortString Type and traditional Pascal The string corresponding to , For forward compatibility

• AnsiString The definition of type is dynamically allocated , With empty characters Null As the end of a string

• String The type can be either ShortString type , It can also be AnsiString type , The default definition is AnsiString type

• stay Delphi The properties of many components in are used String type

2.3 Boolean data type

Boolean data types are used for relational operations and logical operations of conditional statements ,Object Pascal Medium Boolean data type ：

Type the name	type	Number of bytes	Value
Boolean	Boolean type	1	0(False)|1(True)
ByteBool	Byte Boolean	1	0(False)| Not 0(True)
WordBool	Wide Boolean	2	0(False)| Not 0(True)
LongBool	Long Boolean	4	0(False)| Not 0(True)

Boolean The value of type is False and True Two symbolic constants , When programming, try to use Boolean type ; Because other types are set for compatibility with other languages .