@li @ref overview_string_intro
@li @ref overview_string_internal
+@li @ref overview_string_binary
@li @ref overview_string_comparison
@li @ref overview_string_advice
@li @ref overview_string_related
@section overview_string_intro Introduction
wxString is a class which represents a Unicode string of arbitrary length and
-containing arbitrary characters.
-
-The @c NUL character is allowed, but be
-aware that in the current string implementation some methods might not work
-correctly in this case. @todo still true?
+containing arbitrary Unicode characters.
This class has all the standard operations you can expect to find in a string
class: dynamic memory management (string extends to accommodate new
-characters), construction from other strings, C strings, wide character C strings
-and characters, assignment operators, access to individual characters, string
+characters), construction from other strings, compatibility with C strings and
+wide character C strings, assignment operators, access to individual characters, string
concatenation and comparison, substring extraction, case conversion, trimming and
padding (with spaces), searching and replacing and both C-like @c printf (wxString::Printf)
and stream-like insertion functions as well as much more - see wxString for a
@section overview_string_internal Internal wxString encoding
-Since wxWidgets 3.0 wxString internally uses <b>UCS-2</b> (with Unicode
+Since wxWidgets 3.0 wxString internally uses <b>UTF-16</b> (with Unicode
code units stored in @c wchar_t) under Windows and <b>UTF-8</b> (with Unicode
code units stored in @c char) under Unix, Linux and Mac OS X to store its content.
For definitions of <em>code units</em> and <em>code points</em> terms, please
see the @ref overview_unicode_encodings paragraph.
-Note that there is a difference about UCS-2 and UTF-16: the first is a fixed-length
-encoding, without <em>surrogate pairs</em>, while the latter is a
-variable-length encoding. Except for this the two encodings are identical.
-
For simplicity of implementation, wxString when <tt>wxUSE_UNICODE_WCHAR==1</tt>
-(e.g. on Windows) uses UCS-2 and thus doesn't know anything about surrogate pairs;
-it always consider 1 code unit per 1 code point, while this is really true only for
-characters in the @e BMP (Basic Multilingual Plane).
+(e.g. on Windows) uses <em>per code unit indexing</em> instead of
+<em>per code point indexing</em> and doesn't know anything about surrogate pairs;
+in other words it always considers code points to be composed by 1 code point,
+while this is really true only for characters in the @e BMP (Basic Multilingual Plane).
Thus when iterating over a UTF-16 string stored in a wxString under Windows, the user
-code has to take care of <em>surrogate pair</em> handling himself.
+code has to take care of <em>surrogate pairs</em> himself.
(Note however that Windows itself has built-in support for surrogate pairs in UTF-16,
such as for drawing strings on screen.)
+@remarks
+Note that while the behaviour of wxString when <tt>wxUSE_UNICODE_WCHAR==1</tt>
+resembles UCS-2 encoding, it's not completely correct to refer to wxString as
+UCS-2 encoded since you can encode characters outside the @e BMP in a wxString.
+
When instead <tt>wxUSE_UNICODE_UTF8==1</tt> (e.g. on Linux and Mac OS X)
-wxString handles UTF8 multi-bytes sequences just fine, so that you can use
+wxString handles UTF8 multi-bytes sequences just fine also for characters outside
+the BMP (it implements <em>per code point indexing</em>), so that you can use
UTF8 in a completely transparent way:
Example:
wxPrintf("wxString reports a length of %d character(s)", test.length());
// prints "wxString reports a length of 1 character(s)" on Linux
// prints "wxString reports a length of 2 character(s)" on Windows
- // since Windows doesn't have surrogate pairs support!
+ // since wxString on Windows doesn't have surrogate pairs support!
// second test, this time using characters part of the Unicode BMP:
@image html overview_wxstring_encoding.png
-As you can see, UCS2/UTF16 encoding is straightforward (for characters in the @e BMP)
-and in this example the UCS2-encoded wxString takes 8 bytes.
+As you can see, UTF16 encoding is straightforward (for characters in the @e BMP)
+and in this example the UTF16-encoded wxString takes 8 bytes.
UTF8 encoding is more elaborated and in this example takes 7 bytes.
-The type used by wxString to store Unicode code units is called wxStringCharType.
-
In general, for strings containing many latin characters UTF8 provides a big
-advantage in memory footprint respect UTF16, but requires some more processing
-for common operations like e.g. length calculation.
+advantage with regards to the memory footprint respect UTF16, but requires some
+more processing for common operations like e.g. length calculation.
+
+Finally, note that the type used by wxString to store Unicode code units
+(@c wchar_t or @c char) is always @c typedef-ined to be ::wxStringCharType.
+@section overview_string_binary Using wxString to store binary data
+
+wxString can be used to store binary data (even if it contains @c NULs) using the
+functions wxString::To8BitData and wxString::From8BitData.
+
+Beware that even if @c NUL character is allowed, in the current string implementation
+some methods might not work correctly with them.
+
+Note however that other classes like wxMemoryBuffer are more suited to this task.
+For handling binary data you may also want to look at the wxStreamBuffer,
+wxMemoryOutputStream, wxMemoryInputStream classes.
+
@section overview_string_comparison Comparison to Other String Classes
Much work has been done to make existing code using ANSI string literals
work as before version 3.0.
+
If you nonetheless need to have a wxString that uses @c wchar_t
on Unix and Linux, too, you can specify this on the command line with the
@c configure @c --disable-utf8 switch or you can consider using wxUString
or @c std::wstring instead.
+@c wxUSE_UNICODE is now defined as @c 1 by default to indicate Unicode support.
+If UTF-8 is used for the internal storage in wxString, @c wxUSE_UNICODE_UTF8 is
+also defined, otherwise @c wxUSE_UNICODE_WCHAR is.
+See also @ref page_wxusedef_important.
*/
When working with Unicode, it's important to define the meaning of some terms.
-A <b><em>glyph</em></b> is a particular image that represents a character or part
-of a character.
+A <b><em>glyph</em></b> is a particular image (usually part of a font) that
+represents a character or part of a character.
Any character may have one or more glyph associated; e.g. some of the possible
glyphs for the capital letter 'A' are:
which is called <b><em>code point</em></b>; it's typically indicated in documentation
manuals and in the Unicode website as @c U+xxxx where @c xxxx is an hexadecimal number.
-The Unicode standard divides the space of all possible code points in @e planes;
+Note that typically one character is assigned exactly one code point, but there
+are exceptions; the so-called <em>precomposed characters</em>
+(see http://en.wikipedia.org/wiki/Precomposed_character) or the <em>ligatures</em>.
+In these cases a single "character" may be mapped to more than one code point or
+viceversa more characters may be mapped to a single code point.
+
+The Unicode standard divides the space of all possible code points in <b><em>planes</em></b>;
a plane is a range of 65,536 (1000016) contiguous Unicode code points.
Planes are numbered from 0 to 16, where the first one is the @e BMP, or Basic
Multilingual Plane.
More precisely, a code unit is the minimal bit combination that can represent a
unit of encoded text for processing or interchange.
-The @e UTF or Unicode Transformation Formats are algorithms mapping the Unicode
+The <b><em>UTF</em></b> or Unicode Transformation Formats are algorithms mapping the Unicode
code points to code unit sequences. The simplest of them is <b>UTF-32</b> where
each code unit is composed by 32 bits (4 bytes) and each code point is always
represented by a single code unit (fixed length encoding).
However, unlike the Unicode build mode of the previous versions of wxWidgets, this
support is mostly transparent: you can still continue to work with the @b narrow
(i.e. current locale-encoded @c char*) strings even if @b wide
-(i.e. UTF16/UCS2-encoded @c wchar_t* or UTF8-encoded @c char*) strings are also
+(i.e. UTF16-encoded @c wchar_t* or UTF8-encoded @c char*) strings are also
supported. Any wxWidgets function accepts arguments of either type as both
kinds of strings are implicitly converted to wxString, so both
@code
@section overview_unicode_settings Unicode Related Compilation Settings
-@c wxUSE_UNICODE is now defined as 1 by default to indicate Unicode support.
+@c wxUSE_UNICODE is now defined as @c 1 by default to indicate Unicode support.
If UTF-8 is used for the internal storage in wxString, @c wxUSE_UNICODE_UTF8 is
also defined, otherwise @c wxUSE_UNICODE_WCHAR is.
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