AnsiString

AnsiString is a dynamic string type historically used in Borland Pascal, Delphi, and related environments to store text encoded in the 8-bit ANSI character set. It is not Unicode by default and is designed to hold arbitrary 8-bit data as well as text.

One of its defining features is that AnsiString is dynamic and reference-counted with copy-on-write semantics. When an AnsiString value is assigned or passed as a parameter, the underlying data may be shared until one side is modified, at which point a separate copy is created. The memory layout typically includes a reference count and a length prefix followed by the actual character bytes.

Encoding and code pages are central to AnsiString. On Windows, it uses the system ANSI code page (ACP), so the meaning of each byte can depend on the active code page. While it can store any 8-bit data, interpretation as characters depends on code page settings. Conversions between AnsiString and other string types, such as UnicodeString, are supported by the language’s standard library, enabling interoperability with newer Unicode-based code.

Interoperability with external APIs is common: a value of type AnsiString can be passed to procedures expecting PAnsiChar, and assignments can come from PAnsiChar sources. Basic string operations, such as length, concatenation, and slicing, apply to AnsiString as they do to other dynamic string types.

Limitations and evolution: in modern applications, UnicodeString is preferred for multilingual text, while AnsiString remains relevant for legacy code, certain low-level tasks, or binary data. The maximum length on typical 32-bit platforms is substantial (over two billion characters), but memory usage and performance considerations apply due to the underlying reference counting and copy-on-write behavior.

See also: UnicodeString, RawByteString, ShortString, PAnsiChar.