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 ANSI character.
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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.
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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.
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PWideChar
A variable of type PWideChar is a pointer to a WideChar variable.
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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 with the implicit codepage CP_ACP. The length is stored in the character at index 0.
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AnsiString
Ansistrings or UTF8Strings 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.
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UnicodeString
Like AnsiStrings UniCodeStrings are reference counted, null-terminated arrays, but they are implemented as arrays of WideChars instead of regular Chars.
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UTF8String
The type UTF8String is an alias to the type AnsiString.
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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.
WideStrings consist of COM compatible UTF16 encoded bytes on Windows machines (UCS2 on Windows 2000), and they are encoded as plain UTF16 on Linux, Mac OS X and iOS.
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PShortString
A variable of type PShortString is a pointer that points to the first byte of a ShortString-type variable.
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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.
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PUnicodeString
Variables of type PUnicodeString are pointers to variables of type UnicodeString.
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PWideString
Variables of type PWideString are pointers. They point to the first char of a WideString-typed variable.
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