AnsiString: what changed
Revision 1 to 2. Removed lines have a minus sign; added lines have a plus sign.
| Old | New | Line | |
|---|---|---|---|
| 1 | 1 | **`AnsiString`** is a variable-length string [[Data type|data type]]. It can store characters that have a size of one Byte. | |
| 2 | 2 | ||
| 3 | 3 | ## implementation | |
| 4 | 4 | ||
| 5 | 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 | 6 | ||
| 7 | 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 | 8 | ||
| 9 | 9 | - a code page | |
| 10 | 10 | - the size of a character | |
| 11 | 11 | - a reference count | |
| 12 | 12 | - the length of the string. | |
| 13 | 13 | ||
| 14 | - | ||
| 15 | 14 | <tbody> | |
| 16 | - | ||
| 17 | - | ||
| 18 | - | ||
| 19 | - | ||
| 20 | - | ||
| 21 | - | ||
| 22 | - | ||
| 23 | - | ||
| 24 | - | ||
| 25 | - | ||
| 26 | - | ||
| 27 | - | ||
| 28 | - | ||
| 29 | - | ||
| 30 | - | ||
| 31 | - | ||
| 32 | - | ||
| 33 | - | ||
| 34 | - | ||
| 35 | - | ||
| 36 | - | ||
| 37 | - | ||
| 38 | - | ||
| 39 | - | ||
| 40 | - | ||
| 41 | - | ||
| 42 | - | ||
| 43 | - | ||
| 44 | - | ||
| 45 | - | ||
| 15 | + | ||
| 46 | 16 | </tbody> | |
| 47 | - | ||
| 48 | 17 | ||
| 49 | 18 | Only the length field has significance in Pascal. In Pascal, an `AnsiString` may contain `#0` characters. | |
| 50 | 19 | ||
| 51 | 20 | An `AnsiString` can furthermore be associated with a code page (since [[FPC New Features 3.0.0|3.0.0]]). | |
| 52 | 21 | ||
| 53 | 22 | ## application | |
| 54 | 23 | ||
| 55 | 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. | |
| 56 | 25 | ||
| 57 | 26 | Characters in `AnsiString` have a 1-based index. `myAnsiString[1]` refers to the first character. | |
| 58 | 27 | ||
| 59 | 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. | |
| 60 | 29 | ||
| 61 | 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. | |
| 62 | 31 | ||
| 63 | - | ||
| 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. | |
| 64 | 33 | ||
| 65 | 34 | ## caveats | |
| 66 | 35 | ||
| 67 | 36 | - The compiler directive [[$H|{$longStrings on}]] (or `{$H+}`) [[Defensive programming techniques|aliases string]] (without a specified length) to `AnsiString`. | |
| 68 | 37 | - `AnsiString` as a *managed* data type introduces a certain overhead. See [[Avoiding implicit try finally section]] for more explanations. | |
| 69 | 38 | - The [[SizeOf|sizeOf]] value of an `AnsiString` variable is merely the size of a pointer. | |
| 70 | - | ||
| 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. | |
| 71 | 40 | ||
| 72 | 41 | ## see also | |
| 73 | 42 | ||
| 74 | 43 | - [[Character and string types]] | |
| 75 | 44 | - [Ansistrings](https://www.freepascal.org/docs-html/current/ref/refsu9.html#x32-370003.2.4) in the reference guide | |
| 76 | 45 | - [Ansistrings](https://www.freepascal.org/docs-html/current/prog/progsu161.html#x205-2160008.2.7) in the programmer’s guide | |
| 77 | 46 | ||
| 78 | 47 | --- | |
| 79 | 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).* | |
| 80 | 49 | Category: Data types |