Win32 ProgrammingLesson 6: Everything you never wanted to know about strings

Before We Begin Several of you probably had problems with

character types in the last assignment, especially when reading the command line

Why? Because in Windows, strings aren’t always strings (if that makes sense)

Why? Traditionally, a C string is a sequence of

bytes, terminated by a NULL Unfortunately, this only accommodates 256

different characters, and that’s too few for some languages (Kanji being the classic example)

DBCS To fix this problem DBCS was created. In a DBCS each character consists of 1 or 2

bytes This means things like strlen don’t work

correctly Helper functions exist, but the solution is ugly Enter UNICODE

WBCS Wide Byte Character Set == Unicode Consortium founded in 1988(!) See http://www.unicode.org for more

information that you could ever want All characters are 16 bits in length

Why bother? Enables easy data exchange between

languages Create a single binary that supports all

languages Improves execution efficiency

History Unicode really is much more of a Windows

2000 thing… Support in 98 was lacking However, looking to the future, we’ll ignore

the old 16-bit application space Windows CE is Unicode only

Writing Unicode Code… It’s possible to write pure Unicode

applications using several new functions in the RTL

However, you can write code which is *both* very easily using macros

Unicode types typedef unsigned short wchar_t; Declared in string.h wchar_t szBuffer[100] allocates 100

characters but not 100 bytes Breaks strcat, strcpy etc. Equivalent functions with wcs replacing str

e.g. wcscat

A Better Way tchar.h Introduces a series of macros which allows

the program to use Unicode or not, depending on compilation options

Creates a new TYPE TCHAR which is equivalent to a char if _UNICODE is not defined, and a wchar_t if it is

Problems Imagine this:

TCHAR *szError = “Error”; wchar_t *szError = “Error”; TCHAR *szError = L“Error”; TCHAR *szError = _TEXT(“Error”);

Windows Unicode data WCHAR: Unicode character PWSTR: Pointer to a Unicode string PWCSTR: Pointer to a constant Unicode

string

Windows API Revisited CreateWindowEx doesn’t exist… Really, is CreateWindowExA and

CreateWindowExW One is ASCII, the other is Unicode Switched in WinUser.h depending on the

definition of UNICODE

Unicode Gotchas Use type BYTE and PBYTE to define bytes Use generic type TCHAR etc. Use the TEXT macro Beware string arithmetic… don’t think about

sizeof(szBuffer) as the number of characters you can hold! Similarly, think about malloc

Windows functions Use lstrcat, lstrcmp, lstrcmpi, lstrcpy and

lstrlen instead of wcs/str counterparts Some use the Windows function

CompareString Useful for fancy language comparisons There are a whole host of these functions (like

CharLower and CharLowerBuff…)

Type Conversion Of course, sometimes you have to convert

from ASCII to Unicode in a program Use MultiByteToWideChar to make Wide

characters Use WideCharToMultiByte to make regular

characters

Your pwn DLLs You can write your DLLs to provide both

ASCII and Unicode support For example, imagine a routine which

reverses a string… BOOL StringReverseW(PWSTR pWideCharStr)

Instead of writing a completely separate function for StringReverseA… it should convert to WCS and then call StringReverseW and then convert back

Prototype BOOL StringReverseW(PWSTR pWideCharStr);

BOOL StringReverseA(PSTR pMultibyteStr);

#ifdef UNICODE#define StringReverse StringReverseW#else#define StringReverse StringReverseA#endif

Not-too-difficult Assignment Sort n words from the command line in

ascending alphabetic order (unless the –d flag is set , in which case descending), and have your program compile and run easily with MBCS or UNICODE set

Next Class Simple Kernel Objects…