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AnsiString: what changed

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Title: AnsiString Ansistring

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1-**`AnsiString`** is a variable-length string [[Data type|data type]]. It can store characters that have a size of one Byte.
2-
3-## implementation
4-
5-In [[FPC]] an `AnsiString` is implemented as a [[Pointer|pointer]]. It is a managed data type. As such it is initialized with [[Nil|nil]] as soon as it enters the scope. Memory for the character sequence is dynamically allocated and freed.
6-
7-An `AnsiString` points to the *first* character. This facilitates interfacing to libraries or foreign functions expecting [[PChar|pChar strings]]. For that, an `AnsiString` always concludes with a null [[Byte]]. *In [[Pascal]]*, this terminating null Byte has no significance as to the string’s value (including its length). An `AnsiString` always entails some management data *before* the first character. These are
8-
9-- a code page
10-- the size of a character
11-- a reference count
12-- the length of the string.
13-
14-<tbody>
15-
16-</tbody>
17-
18-Only the length field has significance in Pascal. In Pascal, an `AnsiString` may contain `#0` characters.
19-
20-An `AnsiString` can furthermore be associated with a code page (since [[FPC New Features 3.0.0|3.0.0]]).
21-
22-## application
23-
24-The data type `AnsiString` can be used like any other string data type. You may [[Becomes|assign]] string literals to an `AnsiString` variable as normal. String values can be compared ([[Equal|=]]) just as usual. The entire pointer-characteristic is transparent.
25-
26-Characters in `AnsiString` have a 1-based index. `myAnsiString[1]` refers to the first character.
27-
28-> **Note:** The linear character index is only guaranteed to work for strings that have a maximum character size of `1`. That means, using an integer index for example on an UTF-8 encoded string (not exclusively containing ASCII characters) will produce erroneous results.
29-
30-The [`length` function](https://www.freepascal.org/docs-html/rtl/system/length.html), and for that matter also `high`, will return a string’s length by examining the length data field.
31-
32-Because an `AnsiString` is essentially a pointer, *copying* strings of this type is fast, since only the reference is copied and the reference count increased. Modifications may trigger a COW.
33-
34-## caveats
35-
36-- The compiler directive [[$H|{$longStrings on}]] (or `{$H+}`) [[Defensive programming techniques|aliases string]] (without a specified length) to `AnsiString`.
37-- `AnsiString` as a *managed* data type introduces a certain overhead. See [[Avoiding implicit try finally section]] for more explanations.
38-- The [[SizeOf|sizeOf]] value of an `AnsiString` variable is merely the size of a pointer.
39-- Assigning an empty string *to an `AnsiString` variable will in fact assign `nil` to the variable and, if the reference count hit zero, release underlying memory (if any was previously allocated at all). Empty strings are*not'' stored as described above.
40-
41-## see also
42-
43-- [[Character and string types]]
44-- [Ansistrings](https://www.freepascal.org/docs-html/current/ref/refsu9.html#x32-370003.2.4) in the reference guide
45-- [Ansistrings](https://www.freepascal.org/docs-html/current/prog/progsu161.html#x205-2160008.2.7) in the programmer’s guide
46-
47----
48-*From the Free Pascal wiki, page "AnsiString", as it stood on 2023-12-22 after a change by Alextpp, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).*
49-Category: Data types
1+#REDIRECT [[AnsiString]]

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