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Here is a cheat sheet for converting Microsoft C or C++ source code to support Unicode.It does not attempt to explain much and presumes you are generally familiar with Microsoft'sapproach to Unicode. The goal is just to have a single place to look for names, correct spellings, etc.of relevant data types, functions, etc.
Also see: Cheat Sheet: Unicode-enabling Microsoft C/C++ Source Code in Chinese

Unicode glyph cheat sheet Common Unicode characters with digraph or code point, layed out for quick location. Includes general symbols, arrows, drawing characters, and IPA letters. Unicode is a computing standard for the consistent encoding symbols. It was created in 1991. It’s just a table, which shows glyphs position to encoding system. Encoding takes symbol from table, and tells font what should be painted. But computer can understand binary code only. So, encoding is used number 1 or 0 to represent characters.

Initial Steps for Unicode-enabling Microsoft C/C++ Source

• Define _UNICODE, undefine _MBCS if defined.
• Convert literal strings to use L or _T
• Convert string functions to use Wide or TCHAR versions.
• Clarify string lengths in API as byte or character counts.For character-based display or printing (as opposed to GUI which is pixel-based)use column counts, not byte or character.
• Replace character pointer arithmetic with GetNext style, ascharacters may consist of more than one Unicode code unit.
• Watch buffer size and buffer overflows- changing encodingsmay require either larger buffers or limiting string lengths. Ifcharacter size changes from 1 byte to as many as 4 bytes, andstring length was formerly 20 characters and 20 bytes, eitherexpand the string buffer(s) from 20 to 80 bytes or limit thestring to 5 characters (and therefore 20 bytes).Note maximum buffer expansion may be constrained (for example to 65 KB).Reducing string length to a fixed number of characters may break existing applications.Limiting strings to a fixed byte length is dangerous. For example, allowing anystring that fits into 20 bytes. Simple operations such as uppercasinga string may cause it to grow and exceed the byte length.
• Replace functions that accept or return arguments of a single character, with functions that use strings instead.(International) Operations on a single character may result in more than one code point being returned. For example,upper('ß')returns 'SS'.
• Use wmain instead of main.The environment variable is then _wenviron instead of _environ.
  wmain( int argc, wchar_t *argv[ ], wchar_t *envp[ ] ).
• MFC Unicode applications use wWinMain as the entry point.
  In the Output page of the Linker folder in the project's Property Pages dialog box,set the Entry Point symbol to wWinMainCRTStartup.
• Consider fonts. Identify the fonts that will render each language or script used.

File I/O, Database, Transfer Protocol Considerations

• Consider whether to read/write UTF-8 or UTF-16 in files, databases, and for data exchange.
• Consider Endian-ness in UTF-16 files.
  Read/Write Big-Endian on networks. Use Big-Endian if you don't produce a BOM.
  Endian-ness of files will depend on the file format and/or the architectureof the source or target machine.
  When reading files encoded in UTF-16 or UTF-32,be prepared to swap-bytes to convert endian-ness.
  Also consider streams and transfer protocols and the encoding used in each.
• Label files or protocols for data exchange with the correct character encoding.E.g. set HTTP, HTML, XML to UTF-8 or UTF-16.
• Consider Unicode BOM (Byte Order Marker) and whetherit should be written with data. Remove it when reading data.
• Consider encoding conversion of legacy data and files, import and export, transfer protocols.(MultiByteToWideChar,WideCharToMultiByte,mbtowc,wctomb,wctombs,mbstowcs )
• Consider writing to the Clipboard-
  use CF_TEXT format and write native character encoding (ANSI) text, and
  use CF_UNICODETEXT format and write Unicode text.
• Database applications should consider Data Type(NCHAR, NVARCHAR)and Schema Changes, Triggers, Stored Procedures, and Queries. Data Storagegrowth, Indexes and Performance.
  Note that the Unicode schema changes will have different impacts and concerns on different vendors' databases.If database portability is a requirement, the features and behaviors of each database need to be taken into account.
  (I know this item is seriously understated. To be expanded sometime in the future.)

Stream I/O

Streams are difficult in Microsoft C++. You may run into 3 types of problems:

1. Unicode filenames are not supported.The workaround is to useFILE * _wfopen and if needed, use the FILE handle in subsequent stream I/O.
2. Stream I/O will convert Unicode data from/to native (ANSI) code page on read/write,not UTF-8 or UTF-16.However the stream class can be modified to read/write UTF-8.You can implement a facet to convert between Unicode and UTF-8.
   codecvt <wchar_t, char_traits <wchar_t> >
3. To read/write UTF-16 with stream I/O, use binary opens and binary I/O. To set binary I/O:
   Also see the Microsoft run-time library reference: 'Unicode Stream I/O in Text and Binary Modes'.

Note: There aren't TCHAR equivalents forcout/wcout, cin/wcin, etc.You may want to make your own preprocessor definition for 'tout',if you are compiling code both ways.

Internationalization, Advanced Unicode, Platform and Other Considerations

• Consider using locale-based routines and further internationalization.
• For Windows 95, 98 and ME, consider using theMicrosoft MSLU (Microsoft Layer for Unicode)
• Consider string compares and sorting, Unicode Collation Algorithm
• Consider Unicode Normalization
• Consider Character Folding
• Reconsider doing this on your own. Bring in an experiencedUnicode consultant,and deploy your existing resources on the tasks they do best.(Hey, an I18nGuy's gotta earn a living...)

Unicode BOM Encoding Values

Encoding Form BOM Encoding UTF-8 EF BB BF UTF-16 (big-endian) FE FF UTF-16 (little-endian) FF FE UTF-16BE, UTF-32BE (big-endian) No BOM! UTF-16LE, UTF-32LE (little-endian) No BOM! UTF-32 (big-endian) 00 00 FE FF UTF-32 (little-endian) FF FE 00 00 SCSU (compression) 0E FE FF

The Byte Order Marker (BOM) is Unicode character U+FEFF.(It can also represent a Zero Width No-break Space.)The code point U+FFFE is illegal in Unicode, and shouldnever appear in a Unicode character stream. Therefore the BOM can be used in the first characterof a file (or more generally a string), as an indicator of endian-ness. With UTF-16,if the first character is read as bytes FE FF then the texthas the same endian-ness as the machine reading it. If the character is read as bytesFF FE, thenthe endian-ness is reversed and all 16-bit words should be byte-swapped as they are read-in.In the same way, the BOM indicates the endian-ness of text encoded with UTF-32. Note that not all files start with a BOM however. In fact, the Unicode Standard says that text thatdoes not begin with a BOM MUST be interpreted in big-endian form. The character U+FEFF also serves as an encoding signaturefor the Unicode Encoding Forms.The tableshows the encoding of U+FEFF in each of the Unicode encoding forms.Note that by definition, text labeled as UTF-16BE, UTF-32BE, UTF-32LE or UTF-16LE shouldnot have a BOM. The endian-ness isindicated in the label. For text that is compressed with the SCSU (Standard Compression Scheme for Unicode) algorithm,there is also a recommended signature.

Constant and Global Variables

ANSI	Wide	TCHAR
EOF	WEOF	_TEOF
_environ	_wenviron	_tenviron
_pgmptr	_wpgmptr	_tpgmptr

Data Types

ANSI	Wide	TCHAR
char	wchar_t	_TCHAR
_finddata_t	_wfinddata_t	_tfinddata_t
__finddata64_t	__wfinddata64_t	_tfinddata64_t
_finddatai64_t	_wfinddatai64_t	_tfinddatai64_t
int	wint_t	_TINT
signed char	wchar_t	_TSCHAR
unsigned char	wchar_t	_TUCHAR
char	wchar_t	_TXCHAR
L	_T or _TEXT
LPSTR (char *)	LPWSTR (wchar_t *)	LPTSTR (_TCHAR *)
LPCSTR (const char *)	LPCWSTR (const wchar_t *)	LPCTSTR (const _TCHAR *)
LPOLESTR (For OLE)	LPWSTR	LPTSTR

Platform SDK String Functions

There are many Windows API that compile into ANSI or Wide forms,depending on whether the symbol UNICODE isdefined. Modules that operate on both ANSI and Wide characters, need tobe aware of this. Otherwise, using the Character Data Type-independent namerequires no changes, just compile with the symbol UNICODEdefined.

The following list is by no means all of the Character Data Type-dependent API, justsome character and string related ones. Look in WinNLS.h for some code pageand locale related API.

ANSI	Wide	Character Data Type- Independent Name
CharLowerA	CharLowerW	CharLower
CharLowerBuffA	CharLowerBuffW	CharLowerBuff
CharNextA	CharNextW	CharNext
CharNextExA	CharNextExW	CharNextEx
CharPrevA	CharPrevW	CharPrev
CharPrevExA	CharPrevExW	CharPrevEx
CharToOemA	CharToOemW	CharToOem
CharToOemBuffA	CharToOemBuffW	CharToOemBuff
CharUpperA	CharUpperW	CharUpper
CharUpperBuffA	CharUpperBuffW	CharUpperBuff
CompareStringA	CompareStringW	CompareString
FoldStringA	FoldStringW	FoldString
GetStringTypeA	GetStringTypeW	GetStringType
GetStringTypeExA	GetStringTypeExW	GetStringTypeEx
IsCharAlphaA	IsCharAlphaW	IsCharAlpha
IsCharAlphaNumericA	IsCharAlphaNumericW	IsCharAlphaNumeric
IsCharLowerA	IsCharLowerW	IsCharLower
IsCharUpperA	IsCharUpperW	IsCharUpper
LoadStringA	LoadStringW	LoadString
lstrcatA	lstrcatW	lstrcat
lstrcmpA	lstrcmpW	lstrcmp
lstrcmpiA	lstrcmpiW	lstrcmpi
lstrcpyA	lstrcpyW	lstrcpy
lstrcpynA	lstrcpynW	lstrcpyn
lstrlenA	lstrlenW	lstrlen
OemToCharA	OemToCharW	OemToChar
OemToCharBuffA	OemToCharBuffW	OemToCharBuff
wsprintfA	wsprintfW	wsprintf
wvsprintfA	wvsprintfW	wvsprintf

TCHAR String Functions

Functions sorted by ANSI name, for ease of converting to Unicode.

ANSI	Wide	TCHAR
_access	_waccess	_taccess
_atoi64	_wtoi64	_tstoi64
_atoi64	_wtoi64	_ttoi64
_cgets	_cgetws	cgetts
_chdir	_wchdir	_tchdir
_chmod	_wchmod	_tchmod
_cprintf	_cwprintf	_tcprintf
_cputs	_cputws	_cputts
_creat	_wcreat	_tcreat
_cscanf	_cwscanf	_tcscanf
_ctime64	_wctime64	_tctime64
_execl	_wexecl	_texecl
_execle	_wexecle	_texecle
_execlp	_wexeclp	_texeclp
_execlpe	_wexeclpe	_texeclpe
_execv	_wexecv	_texecv
_execve	_wexecve	_texecve
_execvp	_wexecvp	_texecvp
_execvpe	_wexecvpe	_texecvpe
_fdopen	_wfdopen	_tfdopen
_fgetchar	_fgetwchar	_fgettchar
_findfirst	_wfindfirst	_tfindfirst
_findnext64	_wfindnext64	_tfindnext64
_findnext	_wfindnext	_tfindnext
_findnexti64	_wfindnexti64	_tfindnexti64
_fputchar	_fputwchar	_fputtchar
_fsopen	_wfsopen	_tfsopen
_fullpath	_wfullpath	_tfullpath
_getch	_getwch	_gettch
_getche	_getwche	_gettche
_getcwd	_wgetcwd	_tgetcwd
_getdcwd	_wgetdcwd	_tgetdcwd
_ltoa	_ltow	_ltot
_makepath	_wmakepath	_tmakepath
_mkdir	_wmkdir	_tmkdir
_mktemp	_wmktemp	_tmktemp
_open	_wopen	_topen
_popen	_wpopen	_tpopen
_putch	_putwch	_puttch
_putenv	_wputenv	_tputenv
_rmdir	_wrmdir	_trmdir
_scprintf	_scwprintf	_sctprintf
_searchenv	_wsearchenv	_tsearchenv
_snprintf	_snwprintf	_sntprintf
_snscanf	_snwscanf	_sntscanf
_sopen	_wsopen	_tsopen
_spawnl	_wspawnl	_tspawnl
_spawnle	_wspawnle	_tspawnle
_spawnlp	_wspawnlp	_tspawnlp
_spawnlpe	_wspawnlpe	_tspawnlpe
_spawnv	_wspawnv	_tspawnv
_spawnve	_wspawnve	_tspawnve
_spawnvp	_wspawnvp	_tspawnvp
_spawnvpe	_wspawnvpe	_tspawnvpe
_splitpath	_wsplitpath	_tsplitpath
_stat64	_wstat64	_tstat64
_stat	_wstat	_tstat
_stati64	_wstati64	_tstati64
_strdate	_wstrdate	_tstrdate
_strdec	_wcsdec	_tcsdec
_strdup	_wcsdup	_tcsdup
_stricmp	_wcsicmp	_tcsicmp
_stricoll	_wcsicoll	_tcsicoll
_strinc	_wcsinc	_tcsinc
_strlwr	_wcslwr	_tcslwr
_strncnt	_wcsncnt	_tcsnbcnt
_strncnt	_wcsncnt	_tcsnccnt
_strncnt	_wcsncnt	_tcsnccnt
_strncoll	_wcsncoll	_tcsnccoll
_strnextc	_wcsnextc	_tcsnextc
_strnicmp	_wcsnicmp	_tcsncicmp
_strnicmp	_wcsnicmp	_tcsnicmp
_strnicoll	_wcsnicoll	_tcsncicoll
_strnicoll	_wcsnicoll	_tcsnicoll
_strninc	_wcsninc	_tcsninc
_strnset	_wcsnset	_tcsncset
_strnset	_wcsnset	_tcsnset
_strrev	_wcsrev	_tcsrev
_strset	_wcsset	_tcsset
_strspnp	_wcsspnp	_tcsspnp
_strtime	_wstrtime	_tstrtime
_strtoi64	_wcstoi64	_tcstoi64
_strtoui64	_wcstoui64	_tcstoui64
_strupr	_wcsupr	_tcsupr
_tempnam	_wtempnam	_ttempnam
_ui64toa	_ui64tow	_ui64tot
_ultoa	_ultow	_ultot
_ungetch	_ungetwch	_ungettch
_unlink	_wunlink	_tunlink
_utime64	_wutime64	_tutime64
_utime	_wutime	_tutime
_vscprintf	_vscwprintf	_vsctprintf
_vsnprintf	_vsnwprintf	_vsntprintf
asctime	_wasctime	_tasctime
atof	_wtof	_tstof
atoi	_wtoi	_tstoi
atoi	_wtoi	_ttoi
atol	_wtol	_tstol
atol	_wtol	_ttol
character compare	Maps to macro or inline function	_tccmp
character copy	Maps to macro or inline function	_tccpy
character length	Maps to macro or inline function	_tclen
ctime	_wctime	_tctime
fgetc	fgetwc	_fgettc
fgets	fgetws	_fgetts
fopen	_wfopen	_tfopen
fprintf	fwprintf	_ftprintf
fputc	fputwc	_fputtc
fputs	fputws	_fputts
freopen	_wfreopen	_tfreopen
fscanf	fwscanf	_ftscanf
getc	getwc	_gettc
getchar	getwchar	_gettchar
getenv	_wgetenv	_tgetenv
gets	getws	_getts
isalnum	iswalnum	_istalnum
isalpha	iswalpha	_istalpha
isascii	iswascii	_istascii
iscntrl	iswcntrl	_istcntrl
isdigit	iswdigit	_istdigit
isgraph	iswgraph	_istgraph
islead (Always FALSE)	(Always FALSE)	_istlead
isleadbyte (Always FALSE)	isleadbyte (Always FALSE)	_istleadbyte
islegal (Always TRUE)	(Always TRUE)	_istlegal
islower	iswlower	_istlower
isprint	iswprint	_istprint
ispunct	iswpunct	_istpunct
isspace	iswspace	_istspace
isupper	iswupper	_istupper
isxdigit	iswxdigit	_istxdigit
main	wmain	_tmain
perror	_wperror	_tperror
printf	wprintf	_tprintf
putc	putwc	_puttc
putchar	putwchar	_puttchar
puts	_putws	_putts
remove	_wremove	_tremove
rename	_wrename	_trename
scanf	wscanf	_tscanf
setlocale	_wsetlocale	_tsetlocale
sprintf	swprintf	_stprintf
sscanf	swscanf	_stscanf
strcat	wcscat	_tcscat
strchr	wcschr	_tcschr
strcmp	wcscmp	_tcscmp
strcoll	wcscoll	_tcscoll
strcpy	wcscpy	_tcscpy
strcspn	wcscspn	_tcscspn
strerror	_wcserror	_tcserror
strftime	wcsftime	_tcsftime
strlen	wcslen	_tcsclen
strlen	wcslen	_tcslen
strncat	wcsncat	_tcsncat
strncat	wcsncat	_tcsnccat
strncmp	wcsncmp	_tcsnccmp
strncmp	wcsncmp	_tcsncmp
strncpy	wcsncpy	_tcsnccpy
strncpy	wcsncpy	_tcsncpy
strpbrk	wcspbrk	_tcspbrk
strrchr	wcsrchr	_tcsrchr
strspn	wcsspn	_tcsspn
strstr	wcsstr	_tcsstr
strtod	wcstod	_tcstod
strtok	wcstok	_tcstok
strtol	wcstol	_tcstol
strtoul	wcstoul	_tcstoul
strxfrm	wcsxfrm	_tcsxfrm
system	_wsystem	_tsystem
tmpnam	_wtmpnam	_ttmpnam
tolower	towlower	_totlower
toupper	towupper	_totupper
ungetc	ungetwc	_ungettc
vfprintf	vfwprintf	_vftprintf
vprintf	vwprintf	_vtprintf
vsprintf	vswprintf	_vstprintf
WinMain	wWinMain	_tWinMain

References

• 'MSLU: Develop Unicode Applications for Windows 9x Platforms with the Microsoft Layer for Unicode'Michael Kaplan, Cathy Wissink
• 'Design a Single Unicode App that Runs on Both Windows 98 and Windows 2000'F. Avery Bishop, April 1999.
• 'Supporting Multilanguage Text Layout and Complex Scripts with Windows NT 5.0'F. Avery Bishop, David C Brown and Davis M Meltzer, November 1998.
• Newsgroup: MSDN MSLU
• Newsgroup: MSDN Internationalization

Copyright © 2003-2010 Tex Texin. All rights reserved.
Top of page

The tables below are a reference to basic regex. While reading the rest of the site, when in doubt, you can always come back and look here. (It you want a bookmark, here's a direct link to the regex reference tables). I encourage you to print the tables so you have a cheat sheet on your desk for quick reference.
The tables are not exhaustive, for two reasons. First, every regex flavor is different, and I didn't want to crowd the page with overly exotic syntax. For a full reference to the particular regex flavors you'll be using, it's always best to go straight to the source. In fact, for some regex engines (such as Perl, PCRE, Java and .NET) you may want to check once a year, as their creators often introduce new features.
The other reason the tables are not exhaustive is that I wanted them to serve as a quick introduction to regex. If you are a complete beginner, you should get a firm grasp of basic regex syntax just by reading the examples in the tables. I tried to introduce features in a logical order and to keep out oddities that I've never seen in actual use, such as the 'bell character'. With these tables as a jumping board, you will be able to advance to mastery by exploring the other pages on the site.

How to use the tables

The tables are meant to serve as an accelerated regex course, and they are meant to be read slowly, one line at a time. On each line, in the leftmost column, you will find a new element of regex syntax. The next column, 'Legend', explains what the element means (or encodes) in the regex syntax. The next two columns work hand in hand: the 'Example' column gives a valid regular expression that uses the element, and the 'Sample Match' column presents a text string that could be matched by the regular expression.
You can read the tables online, of course, but if you suffer from even the mildest case of online-ADD (attention deficit disorder), like most of us… Well then, I highly recommend you print them out. You'll be able to study them slowly, and to use them as a cheat sheet later, when you are reading the rest of the site or experimenting with your own regular expressions.
Enjoy!
If you overdose, make sure not to miss the next page, which comes back down to Earth and talks about some really cool stuff: The 1001 ways to use Regex.

Regex Accelerated Course and Cheat Sheet

For easy navigation, here are some jumping points to various sections of the page:
✽ Characters
✽ Quantifiers
✽ More Characters
✽ Logic

Unicode Cheat Sheet Free

✽ More White-Space
✽ More Quantifiers
✽ Character Classes
✽ Anchors and Boundaries
✽ POSIX Classes
✽ Inline Modifiers
✽ Lookarounds
✽ Character Class Operations
✽ Other Syntax
(direct link)

Characters

Character	Legend	Example	Sample Match
d	Most engines: one digit from 0 to 9	file_dd	file_25
d	.NET, Python 3: one Unicode digit in any script	file_dd	file_9੩
w	Most engines: 'word character': ASCII letter, digit or underscore	w-www	A-b_1
w	.Python 3: 'word character': Unicode letter, ideogram, digit, or underscore	w-www	字-ま_۳
w	.NET: 'word character': Unicode letter, ideogram, digit, or connector	w-www	字-ま‿۳
s	Most engines: 'whitespace character': space, tab, newline, carriage return, vertical tab	asbsc	a b c
s	.NET, Python 3, JavaScript: 'whitespace character': any Unicode separator	asbsc	a b c
D	One character that is not a digit as defined by your engine's d	DDD	ABC
W	One character that is not a word character as defined by your engine's w	WWWWW	*-+=)
S	One character that is not a whitespace character as defined by your engine's s	SSSS	Yoyo

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Quantifiers

Quantifier	Legend	Example	Sample Match
+	One or more	Version w-w+	Version A-b1_1
{3}	Exactly three times	D{3}	ABC
{2,4}	Two to four times	d{2,4}	156
{3,}	Three or more times	w{3,}	regex_tutorial
*	Zero or more times	A*B*C*	AAACC
?	Once or none	plurals?	plural

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More Characters

Character	Legend	Example	Sample Match
.	Any character except line break	a.c	abc
.	Any character except line break	.*	whatever, man.
.	A period (special character: needs to be escaped by a )	a.c	a.c
	Escapes a special character	.*+? $^/	.*+? $^/
	Escapes a special character	[{()}]	[{()}]

(direct link)

Logic

Logic	Legend	Example	Sample Match
|	Alternation / OR operand	22|33	33
( … )	Capturing group	A(nt|pple)	Apple (captures 'pple')
1	Contents of Group 1	r(w)g1x	regex
2	Contents of Group 2	(dd)+(dd)=2+1	12+65=65+12
(?: … )	Non-capturing group	A(?:nt|pple)	Apple

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More White-Space

Character	Legend	Example	Sample Match
t	Tab	Ttw{2}	T ab
r	Carriage return character	see below
n	Line feed character	see below
rn	Line separator on Windows	ABrnCD	AB CD
N	Perl, PCRE (C, PHP, R…): one character that is not a line break	N+	ABC
h	Perl, PCRE (C, PHP, R…), Java: one horizontal whitespace character: tab or Unicode space separator
H	One character that is not a horizontal whitespace
v	.NET, JavaScript, Python, Ruby: vertical tab
v	Perl, PCRE (C, PHP, R…), Java: one vertical whitespace character: line feed, carriage return, vertical tab, form feed, paragraph or line separator
V	Perl, PCRE (C, PHP, R…), Java: any character that is not a vertical whitespace
R	Perl, PCRE (C, PHP, R…), Java: one line break (carriage return + line feed pair, and all the characters matched by v)

(direct link)

More Quantifiers

Quantifier	Legend	Example	Sample Match
+	The + (one or more) is 'greedy'	d+	12345
?	Makes quantifiers 'lazy'	d+?	1 in 12345
*	The * (zero or more) is 'greedy'	A*	AAA
?	Makes quantifiers 'lazy'	A*?	empty in AAA
{2,4}	Two to four times, 'greedy'	w{2,4}	abcd
?	Makes quantifiers 'lazy'	w{2,4}?	ab in abcd

(direct link)

Character Classes

Character	Legend	Example	Sample Match
[ … ]	One of the characters in the brackets	[AEIOU]	One uppercase vowel
[ … ]	One of the characters in the brackets	T[ao]p	Tap or Top
-	Range indicator	[a-z]	One lowercase letter
[x-y]	One of the characters in the range from x to y	[A-Z]+	GREAT
[ … ]	One of the characters in the brackets	[AB1-5w-z]	One of either: A,B,1,2,3,4,5,w,x,y,z
[x-y]	One of the characters in the range from x to y	[ -~]+	Characters in the printable section of the ASCII table.
[^x]	One character that is not x	[^a-z]{3}	A1!
[^x-y]	One of the characters not in the range from x to y	[^ -~]+	Characters that are not in the printable section of the ASCII table.
[dD]	One character that is a digit or a non-digit	[dD]+	Any characters, inc- luding new lines, which the regular dot doesn't match
[x41]	Matches the character at hexadecimal position 41 in the ASCII table, i.e. A	[x41-x45]{3}	ABE

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Anchors and Boundaries

Anchor	Legend	Example	Sample Match
^	Start of string or start of line depending on multiline mode. (But when [^inside brackets], it means 'not')	^abc .*	abc (line start)
$	End of string or end of line depending on multiline mode. Many engine-dependent subtleties.	.*? the end$	this is the end
A	Beginning of string (all major engines except JS)	Aabc[dD]*	abc (string... ...start)
z	Very end of the string Not available in Python and JS	the endz	this is...n...the end
Z	End of string or (except Python) before final line break Not available in JS	the endZ	this is...n...the endn
G	Beginning of String or End of Previous Match .NET, Java, PCRE (C, PHP, R…), Perl, Ruby
b	Word boundary Most engines: position where one side only is an ASCII letter, digit or underscore	Bob.*bcatb	Bob ate the cat
b	Word boundary .NET, Java, Python 3, Ruby: position where one side only is a Unicode letter, digit or underscore	Bob.*bкошкаb	Bob ate the кошка
B	Not a word boundary	c.*BcatB.*	copycats

(direct link)

POSIX Classes

Character	Legend	Example	Sample Match
[:alpha:]	PCRE (C, PHP, R…): ASCII letters A-Z and a-z	[8[:alpha:]]+	WellDone88
[:alpha:]	Ruby 2: Unicode letter or ideogram	[[:alpha:]d]+	кошка99
[:alnum:]	PCRE (C, PHP, R…): ASCII digits and letters A-Z and a-z	[[:alnum:]]{10}	ABCDE12345
[:alnum:]	Ruby 2: Unicode digit, letter or ideogram	[[:alnum:]]{10}	кошка90210
[:punct:]	PCRE (C, PHP, R…): ASCII punctuation mark	[[:punct:]]+	?!.,:;
[:punct:]	Ruby: Unicode punctuation mark	[[:punct:]]+	‽,:〽⁆

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Inline Modifiers

None of these are supported in JavaScript. In Ruby, beware of (?s) and (?m).

Modifier	Legend	Example	Sample Match
(?i)	Case-insensitive mode (except JavaScript)	(?i)Monday	monDAY
(?s)	DOTALL mode (except JS and Ruby). The dot (.) matches new line characters (rn). Also known as 'single-line mode' because the dot treats the entire input as a single line	(?s)From A.*to Z	From A to Z
(?m)	Multiline mode (except Ruby and JS) ^ and $ match at the beginning and end of every line	(?m)1rn^2$rn^3$	1 2 3
(?m)	In Ruby: the same as (?s) in other engines, i.e. DOTALL mode, i.e. dot matches line breaks	(?m)From A.*to Z	From A to Z
(?x)	Free-Spacing Mode mode (except JavaScript). Also known as comment mode or whitespace mode	(?x) # this is a # comment abc # write on multiple # lines [ ]d # spaces must be # in brackets	abc d
(?n)	.NET, PCRE 10.30+: named capture only	Turns all (parentheses) into non-capture groups. To capture, use named groups.
(?d)	Java: Unix linebreaks only	The dot and the ^ and $ anchors are only affected by n
(?^)	PCRE 10.32+: unset modifiers	Unsets ismnx modifiers

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Lookarounds

Lookaround	Legend	Example	Sample Match
(?=…)	Positive lookahead	(?=d{10})d{5}	01234 in 0123456789
(?<=…)	Positive lookbehind	(?<=d)cat	cat in 1cat
(?!…)	Negative lookahead	(?!theatre)thew+	theme
(?<!…)	Negative lookbehind	w{3}(?<!mon)ster	Munster

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Character Class Operations

Class Operation	Legend	Example	Sample Match
[…-[…]]	.NET: character class subtraction. One character that is in those on the left, but not in the subtracted class.	[a-z-[aeiou]]	Any lowercase consonant
[…-[…]]	.NET: character class subtraction.	[p{IsArabic}-[D]]	An Arabic character that is not a non-digit, i.e., an Arabic digit
[…&&[…]]	Java, Ruby 2+: character class intersection. One character that is both in those on the left and in the && class.	[S&&[D]]	An non-whitespace character that is a non-digit.
[…&&[…]]	Java, Ruby 2+: character class intersection.	[S&&[D]&&[^a-zA-Z]]	An non-whitespace character that a non-digit and not a letter.
[…&&[^…]]	Java, Ruby 2+: character class subtraction is obtained by intersecting a class with a negated class	[a-z&&[^aeiou]]	An English lowercase letter that is not a vowel.
[…&&[^…]]	Java, Ruby 2+: character class subtraction	[p{InArabic}&&[^p{L}p{N}]]	An Arabic character that is not a letter or a number

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Other Syntax

Syntax	Legend	Example	Sample Match
K	Keep Out Perl, PCRE (C, PHP, R…), Python's alternate regex engine, Ruby 2+: drop everything that was matched so far from the overall match to be returned	prefixKd+	12
Q…E	Perl, PCRE (C, PHP, R…), Java: treat anything between the delimiters as a literal string. Useful to escape metacharacters.	Q(C++ ?)E	(C++ ?)

The 1001 ways to use Regex

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