Character and string types

Free Pascal supports several types of characters and strings.

AnsiChar

A variable of type AnsiChar, also referred to as char, is exactly 1 byte in size, and contains one ASCII character.

a

Reference

• FPC AnsiChar documentation

WideChar

A variable of type WideChar, also referred to as UnicodeChar. is exactly 2 bytes in size, and contains one (part of) Unicode character in UTF-16 encoding. Note: it is impossible to encode all Unicode code points in 2 bytes. Therefore, 2 WideChars may be needed to encode a single code point.

a

References

• FPC WideChar documentation
• UTF-16 information on Wikipedia
• RTL UnicodeChar documentation

PChar

A variable of type PChar is basically a pointer to a Char type, but allows additional operations. PChars can be used to access C-style null-terminated strings, e.g. in interaction with certain OS libraries or third-party software.

a	b	c	#0
^

Reference

• FPC PChar documentation

PWideChar

A variable of type PWideChar is a pointer to a WideChar variable.

	a		b		c	#0	#0
^

Reference

• RTL PWideChar documentation

String

The type string may refer to ShortString or AnsiString, depending from the {$H} switch. If the switch is off ({$H-}) then any string declaration will define a ShortString. It size will be 255 chars, if not otherwise specified. If it is on ({$H+}) string without length specifier will define an AnsiString, otherwise a ShortString with specified length.

ShortString

Short strings have a maximum length of 255 characters. The length is stored in the character at index 0.

#3

a

b

c

Reference

• FPC ShortString documentation

AnsiString

Ansistrings are strings that have no length limit. They are reference counted and are guaranteed to be null terminated. Internally, a variable of type AnsiString is treated as a pointer: the actual content of the string is stored on the heap, as much memory as needed to store the string content is allocated.

								a	b	c	#0
RefCount				Length

Reference

• FPC AnsiString documentation

UnicodeString

Like AnsiStrings UniCodeStrings are reference counted, null-terminated arrays, but they are implemented as arrays of WideChars instead of regular Chars.

a

b

c

#0

#0

RefCount

Length

Reference

• FPC UnicodeString documentation

WideString

Variables of type WideString (used to represent unicode character strings in COM applications) resemble those of type UnicodeString, but unlike them they are not reference-counted. On Windows they are allocated with a special windows function which allows them to be used for OLE automation.

				a		b		c	#0	#0
Length

Reference

• FPC WideString documentation

PShortString

A variable of type PShortString is a pointer that points to the first byte of a ShortString-type variable.

#3	a	b	c
^

Reference

• RTL PShortString documentation

PAnsiString

Variables of type PAnsiString are pointers to AnsiString-type variables. However, unlike PShortString-type variables they don't point to the first byte of the header, but to the first char of the AnsiString.

								a	b	c	#0
RefCount				Length				^

Reference

• RTL PAnsiString documentation