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Update wxString overview

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git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53683 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
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Robert Roebling 2008-05-21 08:12:22 +00:00
parent 77da37be72
commit 47e1c61bb7
1 changed files with 15 additions and 46 deletions
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61
docs/doxygen/overviews/string.h
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@ -16,7 +16,6 @@ Classes: wxString, wxArrayString, wxStringTokenizer
@li @ref overview_string_comparison
@li @ref overview_string_advice
@li @ref overview_string_related
@li @ref overview_string_refcount
@li @ref overview_string_tuning
@ -54,13 +53,10 @@ memory for C strings; working with fixed size buffers almost inevitably leads
to buffer overflows. At last, C++ has a standard string class (std::string). So
why the need for wxString? There are several advantages:
@li <b>Efficiency:</b> This class was made to be as efficient as possible: both in
terms of size (each wxString objects takes exactly the same space as a
<tt>char*</tt> pointer, see @ref overview_string_refcount
"reference counting") and speed. It also provides performance
@ref overview_string_tuning "statistics gathering code" which may be
enabled to fine tune the memory allocation strategy for your particular
application - and the gain might be quite big.
@li <b>Efficiency:</b> Since wxWidgets 3.0 wxString uses std::string (UTF8
mode under Linux, Unix and OS X) or std::wstring (MSW) internally by
default to store its constent. wxString will therefore inherit the
performance characteristics from std::string.
@li <b>Compatibility:</b> This class tries to combine almost full compatibility
with the old wxWidgets 1.xx wxString class, some reminiscence to MFC
CString class and 90% of the functionality of std::string class.
@ -70,9 +66,8 @@ why the need for wxString? There are several advantages:
wxString::Printf. Of course, all the standard string operations are
supported as well.
@li <b>Unicode wxString is Unicode friendly:</b> it allows to easily convert to
and from ANSI and Unicode strings in any build mode (see the
@ref overview_unicode "unicode overview" for more details) and maps to
either @c string or @c wstring transparently depending on the current mode.
and from ANSI and Unicode strings (see the @ref overview_unicode "unicode overview"
for more details) and maps to @c wstring transparently.
@li <b>Used by wxWidgets:</b> And, of course, this class is used everywhere
inside wxWidgets so there is no performance loss which would result from
conversions of objects of any other string class (including std::string) to
@ -80,7 +75,7 @@ why the need for wxString? There are several advantages:
However, there are several problems as well. The most important one is probably
that there are often several functions to do exactly the same thing: for
example, to get the length of the string either one of @c length(),
example, to get the length of the string either one of wxString::length(),
wxString::Len() or wxString::Length() may be used. The first function, as
almost all the other functions in lowercase, is std::string compatible. The
second one is the "native" wxString version and the last one is the wxWidgets
@ -144,9 +139,8 @@ easy, just make the function return wxString instead of a C string.
This leads us to the following general advice: all functions taking string
arguments should take <tt>const wxString</tt> (this makes assignment to the
strings inside the function faster because of
@ref overview_string_refcount "reference counting") and all functions returning
strings should return wxString - this makes it safe to return local variables.
strings inside the function faster) and all functions returning strings
should return wxString - this makes it safe to return local variables.
@section overview_string_related String Related Functions and Classes
@ -182,36 +176,11 @@ is vastly better from a performance point of view than a wxObjectArray of
wxStrings.
@section overview_string_refcount Reference Counting and Why You Shouldn't Care
All considerations for wxObject-derived
@ref overview_refcount "reference counted" objects are valid also for wxString,
even if it does not derive from wxObject.
Probably the unique case when you might want to think about reference counting
is when a string character is taken from a string which is not a constant (or
a constant reference). In this case, due to C++ rules, the "read-only"
@c operator[] (which is the same as wxString::GetChar()) cannot be chosen and
the "read/write" @c operator[] (the same as wxString::GetWritableChar()) is
used instead. As the call to this operator may modify the string, its data is
unshared (COW is done) and so if the string was really shared there is some
performance loss (both in terms of speed and memory consumption). In the rare
cases when this may be important, you might prefer using wxString::GetChar()
instead of the array subscript operator for this reasons. Please note that
wxString::at() method has the same problem as the subscript operator in this
situation and so using it is not really better. Also note that if all string
arguments to your functions are passed as <tt>const wxString</tt> (see the
@ref overview_string_advice section) this situation will almost never arise
because for constant references the correct operator is called automatically.
@section overview_string_tuning Tuning wxString for Your Application
@note This section is strictly about performance issues and is absolutely not
necessary to read for using wxString class. Please skip it unless you feel
familiar with profilers and relative tools. If you do read it, please also
read the preceding section about
@ref overview_string_refcount "reference counting".
familiar with profilers and relative tools.
For the performance reasons wxString doesn't allocate exactly the amount of
memory needed for each string. Instead, it adds a small amount of space to each
@ -223,13 +192,13 @@ subsequently adding one character at a time to it, as for example in:
// delete all vowels from the string
wxString DeleteAllVowels(const wxString& original)
{
wxString vowels( "aeuioAEIOU" );
wxString result;
size_t len = original.length();
for ( size_t n = 0; n < len; n++ )
wxString::const_iterator i;
for ( i = original.begin(); i != original.end(); ++i )
{
if ( strchr("aeuio", tolower(original[n])) == NULL )
result += original[n];
if (vowels.Find( *i ) == wxNOT_FOUND)
result += *i;
}
return result;