\section{wxString overview}\label{wxstringoverview}
-Classes: \helpref{wxString}{wxstring}, \helpref{wxArrayString}{wxarray}, \helpref{wxStringTokenizer}{wxstringtokenizer}
+Classes: \helpref{wxString}{wxstring}, \helpref{wxArrayString}{wxarraystring}, \helpref{wxStringTokenizer}{wxstringtokenizer}
\subsection{Introduction}
-wxString is a class which represents a character string of arbitrary (limited by
-{\it MAX\_INT} which is usually 2147483647 on 32 bit machines) length and containing
-arbitrary characters (i.e. ASCII NUL character is allowed, although care should be
-taken when passing strings containing it to other functions).
+wxString is a class which represents a character string of arbitrary length (limited by
+{\it MAX\_INT} which is usually 2147483647 on 32 bit machines) and containing
+arbitrary characters. The ASCII NUL character is allowed, although care should be
+taken when passing strings containing it to other functions.
-wxString only works with ASCII (8 bit characters) strings as of this release,
-however support for UNICODE (16 but characters) is planned for the next one.
+wxString works with both ASCII (8 bit characters) as well as UNICODE (16 but
+characters) strings.
-This class has all standard operations you can expect to find in a string class:
-dynamic memory management (string extends to accomodate new 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 and characters, assignment operators,
-access to separate characters, string concatenation and comparison, substring
+access to individual characters, string concatenation and comparison, substring
extraction, case conversion, trimming and padding (with spaces), searching and
replacing and both C-like \helpref{Printf()}{wxstringprintf} and stream-like
-insertion functions as well as much else - see \helpref{wxString}{wxstring}
-for the list of all functions.
+insertion functions as well as much more - see \helpref{wxString}{wxstring}
+for a list of all functions.
\subsection{Comparison of wxString to other string classes}
The advantages of using a special string class instead of working directly with
-C strings are so obvious (the most imoprtant being, of course, the need to always
-remember to allocate/free memory for C strings unless the programmer prefers
-working with fixed size buffers which almost certainly leads to the dreaded
-buffer overflows) that there is a huge number of such classes available and now,
-finally, C++ even has one (std::string) in standard. Why use wxString then?
+C strings are so obvious that there is a huge number of such classes available.
+The most important advantage is the need to always
+remember to allocate/free 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:
\begin{enumerate}\itemsep=0pt
-\item {\bf Efficiency} {This class was made to be as efficient as possible: both
-in terms of size (each wxString objects takes exactly the same place as {\it
-char *} pointer, \helpref{reference counting}{wxstringrefcount}) and speed.
+\item {\bf Efficiency} 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 {\it
+char *} pointer, sing \helpref{reference counting}{wxstringrefcount}) and speed.
It also provides performance \helpref{statistics gathering code}{wxstringtuning}
which may be enabled to fine tune the memory allocation strategy for your
-particular application - and the gain might be quite big.}
-\item {\bf Compatibility} {This class tries to combine almost full compatibility
+particular application - and the gain might be quite big.
+\item {\bf Compatibility} This class tries to combine almost full compatibility
with the old wxWindows 1.xx wxString class, some reminiscence to MFC CString
-class and 90\% of functionality of std::string class.}
-\item {\bf Rich set of functions} {Some of the functions present in wxString are
+class and 90\% of the functionality of std::string class.
+\item {\bf Rich set of functions} Some of the functions present in wxString are
very useful but don't exist in most of other string classes: for example,
\helpref{AfterFirst}{wxstringafterfirst},
-\helpref{BeforLast}{wxstringbeforlast}, \helpref{operator<<}{wxstringoperator}
+\helpref{BeforeLast}{wxstringbeforelast}, \helpref{operator<<}{wxstringoperatorout}
or \helpref{Printf}{wxstringprintf}. Of course, all the standard string
-operations are supported as well.}
-\item {\bf UNICODE} {In this release, wxString only supports construction from
-an UNICODE string, but in the next one it will be capable of also storing its
-internal data in either ASCII or UNICODE format.}
-\item {\bf Used by wxWindows} {And, of course, this class is used everywhere
+operations are supported as well.
+\item {\bf UNICODE} In this release, wxString only supports {\it construction} from
+a UNICODE string, but in the next one it will be capable of also storing its
+internal data in either ASCII or UNICODE format.
+\item {\bf Used by wxWindows} And, of course, this class is used everywhere
inside wxWindows so there is no performance loss which would result from
conversions of objects of any other string class (including std::string) to
-wxString internally by wxWindows.}
+wxString internally by wxWindows.
\end{enumerate}
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
-\helpref{length()}{wxstringlength}, \helpref{Len()}{wxstringlen} or
-\helpref{Length()}{wxstringLength} may be used. The first function, as almost
+length(), \helpref{Len()}{wxstringlen} or
+\helpref{Length()}{wxstringlength} may be used. The first function, as almost
all the other functions in lowercase, is std::string compatible. The second one
is "native" wxString version and the last one is wxWindows 1.xx way. So the
question is: which one is better to use? And the answer is that:
when used outside wxWindows) and by staying compatible with future versions of
wxWindows which will probably start using std::string sooner or later too.
-In the situations when there is no correspondinw std::string function, please
+In the situations where there is no corresponding std::string function, please
try to use the new wxString methods and not the old wxWindows 1.xx variants
-which are deprecated and risk to disappear in future versions.
+which are deprecated and may disappear in future versions.
-\subsection{Some advices about using wxString}\label{wxstringadvices}
+\subsection{Some advice about using wxString}\label{wxstringadvices}
-Probably main trap with using this class is the implicit conversion operator to
+Probably the main trap with using this class is the implicit conversion operator to
{\it const char *}. It is advised that you use \helpref{c\_str()}{wxstringcstr}
-instead of it to clearly indicate when the conversion is done. Specifically, the
+instead to clearly indicate when the conversion is done. Specifically, the
danger of this implicit conversion may be seen in the following code fragment:
\begin{verbatim}
-
// this function converts the input string to uppercase, output it to the screen
// and returns the result
const char *SayHELLO(const wxString& input)
return output;
}
-
\end{verbatim}
-There are two nasty bugs in these three lines. First of them is in the call to
+There are two nasty bugs in these three lines. First of them is in the call to the
{\it printf()} function. Although the implicit conversion to C strings is applied
-automatically by the compiler in case of
+automatically by the compiler in the case of
\begin{verbatim}
puts(output);
\end{verbatim}
-because the argument of {\it puts()} is known to be of the type {\it const char
-*}, this is {\bf not} done for {\it printf()} which is a function with variable
+because the argument of {\it puts()} is known to be of the type {\it const char *},
+this is {\bf not} done for {\it printf()} which is a function with variable
number of arguments (and whose arguments are of unknown types). So this call may
do anything at all (including displaying the correct string on screen), although
the most likely result is a program crash. The solution is to use
used again, so the code compiles, but as it returns a pointer to a buffer
belonging to a local variable which is deleted as soon as the function exits,
its contents is totally arbitrary. The solution to this problem is also easy:
-just make the function return wxString instead of C string.
+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 {\it const wxString\&} (this makes assignment to the
\subsection{Other string related functions and classes}
-As any program operates with character strings, the standard C library provides quite a
-few of functions to work with them. Unfortunately, some of them have rather non
-intuitive behaviour (like strncpy() which doesn't always terminate the resulting
-string with a NUL) and are in general not very safe (passing NULL to them will
-probably lead to program crash). Moreover, some of very useful functions are not
-standard at all. This is why in addition to all wxString functions, there are
-also a few of global string functions which try to correct these problems:
-\helpref{IsEmpty()}{isempty} verifies whether the string is empty (returning
-TRUE for NULL pointers), \helpref{Strlen()}{strlen} also handles NULLs correctly
-and returns 0 for them and \helpref{Stricmp()}{stricmp} is just a
-platform-independent version of case-insensitive string comparison function
-known either as stricmp() or strcasecmp() on different platforms.
+As most programs use character strings, the standard C library provides quite
+a few functions to work with them. Unfortunately, some of them have rather
+counter-intuitive behaviour (like strncpy() which doesn't always terminate the
+resulting string with a NULL) and are in general not very safe (passing NULL
+to them will probably lead to program crash). Moreover, some very useful
+functions are not standard at all. This is why in addition to all wxString
+functions, there are also a few global string functions which try to correct
+these problems: \helpref{wxIsEmpty()}{wxisempty} verifies whether the string
+is empty (returning {\tt TRUE} for {\tt NULL} pointers),
+\helpref{wxStrlen()}{wxstrlen} also handles NULLs correctly and returns 0 for
+them and \helpref{wxStricmp()}{wxstricmp} is just a platform-independent
+version of case-insensitive string comparison function known either as
+stricmp() or strcasecmp() on different platforms.
+
+The {\tt <wx/string.h>} header also defines \helpref{wxSnprintf}{wxsnprintf}
+and \helpref{wxVsnprintf}{wxvsnprintf} functions which should be used instead
+of the inherently dangerous standard {\tt sprintf()} and which use {\tt
+snprintf()} instead which does buffer size checks whenever possible. Of
+course, you may also use \helpref{wxString::Printf}{wxstringprintf} which is
+also safe.
There is another class which might be useful when working with wxString:
\helpref{wxStringTokenizer}{wxstringtokenizer}. It is helpful when a string must
-be broken into tokens and replaces advatageously the standard C library {\it
+be broken into tokens and replaces the standard C library {\it
strtok()} function.
-And the very last string related class is \helpref{wxArrayString}{wxarray}: it
-is just a version of "template" dynamic array class which is specialized to work
-with strings. Please note that this class is specially optimized (it uses its
-knowledge of internal structure of wxString) for storing strigns and so it is
-vastly better from performance point of view than wxObjectArray of wxString.
+And the very last string-related class is \helpref{wxArrayString}{wxarraystring}: it
+is just a version of the "template" dynamic array class which is specialized to work
+with strings. Please note that this class is specially optimized (using its
+knowledge of the internal structure of wxString) for storing strings and so it is
+vastly better from a performance point of view than a wxObjectArray of wxStrings.
\subsection{Reference counting and why you shouldn't care about it}\label{wxstringrefcount}
wxString objects use a technique known as {\it copy on write} (COW). This means
that when a string is assigned to another, no copying really takes place: only
-the reference count on the shared string data is increased and both strings
+the reference count on the shared string data is incremented and both strings
share the same data.
But as soon as one of the two (or more) strings is modified, the data has to be
copied because the changes to one of the strings shouldn't be seen in the
-otheres. As data copying only happens when the string is written to, this is
+others. As data copying only happens when the string is written to, this is
known as COW.
What is important to understand is that all this happens absolutely
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" {\it operator[]} (which is the same as
-\helpref{GetChar()}{wxstringgetchar}) cannot be chosen and the "read/write"
+\helpref{GetChar()}{wxstringgetchar}) cannot be chosen and the "read/write"
{\it operator[]} (the same as
\helpref{GetWritableChar()}{wxstringgetwritablechar}) 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 \helpref{GetChar()}{wxstringgetchar} instead
-of array subscript operator for this reasons. Please note that
-\helpref{at()}{wxstringat} method has the same problem as subscript operator in
+of the array subscript operator for this reasons. Please note that
+\helpref{at()}{wxstringat} 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 {\it const wxString\&} (see the
-section \helpref{Some advices}{wxstringadvices}) this situation will almost
+section \helpref{Some advice}{wxstringadvices}) this situation will almost
never arise because for constant references the correct operator is called automatically.
\subsection{Tuning wxString for your application}\label{wxstringtuning}
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
-\helpref{reference counting}{wxstringrefcounting}.}
+\helpref{reference counting}{wxstringrefcount}.}
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
-allocated block which allows it to not reallocate memory (this is a relatively
+allocated block which allows it to not reallocate memory (a relatively
expensive operation) too often as when, for example, a string is constructed by
subsequently adding one character at a time to it, as for example in:
\begin{verbatim}
-
// delete all vowels from the string
wxString DeleteAllVowels(const wxString& original)
{
return result;
}
-
\end{verbatim}
-This is a quite common situation and not allocating extra memory at all would
+This is quite a common situation and not allocating extra memory at all would
lead to very bad performance in this case because there would be as many memory
(re)allocations as there are consonants in the original string. Allocating too
much extra memory would help to improve the speed in this situation, but due to
them on stderr on program termination. This will show you the average length of
strings your program manipulates, their average initial length and also the
percent of times when memory wasn't reallocated when string concatenation was
-done but the alread preallocated memory was used (this value should be about
+done but the already preallocated memory was used (this value should be about
98\% for the default allocation policy, if it is less than 90\% you should
really consider fine tuning wxString for your application).
projects / wxWidgets.git / blobdiff