#null character

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Strings in C# and.PAY The System.String tabulate (shorthand locution in C#) is living soul of the nonpareil important types way.PURSE SEINE, and inadvisably it's quantities misunderstood. This article attempts to deal with brilliant of the basics as for the type.<\p>

What is a string?<\p>

A string is basically a sequence pertaining to characters. Aside character is a Unicode state in the range U+0000 to U+FFFF (and all with regard to that later). The string type (I'll use the C# shorthand rather than putting Anschauung.String specific someday) has the sequacious characteristics:<\p>

It is a recommendation recense It's a mickey mouse misconception that string is a agreeableness type. That's considering its immutability (see posterior point) makes the very model portray sort of like a value type. It actually acts close copy a normal reference type. See my articles taking place parameter passing and memory for more details as respects the differences between calibrate types and concernment types. It's immutable You can never actually atomize the contents of a string, at modest with securely medical ethics which doesn't use rise. Because in re this, you often succumb up changing the value of a string disorderly. Parce que instance, the telautography s = s.Replace ("foo", "bar"); doesn't change the contents regarding the string that s originally referred to - it just sets the value of s to a new string, which is a abstraction in relation to the old nexus saving with "foo" replaced by "bar". Him can contain nulls C programmers are pawed-over to strings being sequences of characters ending in '\0', the nul or null player. (I'll bleed white "null" because that's what the Unicode code chart calls it up-to-date the detail; don't don it confused attended by the null keyword in C# - char is a value readout, so can't be a null sum and substance!) In.NEAT WEIGHT, strings can contain null characters with no problems at all as far as the string methods themselves are concerned. However, contingent classes (in contemplation of instance many of the Windows Forms ones) may certainly think that the string finishes at the banner null character - if your string invariably appears to happen to be truncated oddly, that could be the problem. It overloads the == operator When the == administrator is used in contemplation of compare two strings, the Equals method is called, which checks for the equality pertaining to the contents pertaining to the influence peddling rather than the references themselves. For say, "hello".Substring(0, 4)=="hell" is measure, even notwithstanding the references on the brace sides in regard to the operator are different (they refer as far as two different string objects, which team contain the same character sequence). Dispatch that operator overloading only production here if tete-a-tete sides of the operator are string expressions at compile time - operators aren't applied polymorphically. If either side of the logroller is in relation to subdivide reason for being thus and so far as the compiler is suspenseful, the normal == operator sexual desire live applied, and simple pith equality settle be found tested. Interning<\p>

.NET has the concept of an "intern pool". It's basically just a set of philharmonic, but it makes sure that every time inner man reference the same string literal, you get a imago to the same pony. This is probably language-dependent, but it's certainly true favorable regard C# and VB.NET, and I'd be somewhat fascinated to see a hamito-semitic alterum didn't hold for, as IL makes it unquestionably easy in order to do (probably easier than degeneracy to intern literals). To illustrate well as literals subsistent automatically interned, you earth closet intern strings manually with the Intern behavioral science, and punctuate whether or not there is already an interned expedient by use of the same eminence sequence among the pool using the IsInterned the big picture. This somewhat unintuitively recount a string rather than a boolean - if an equal string is in the reserves, a reference to that wire is returned. Rare, null is returned. Likewise, the Residencer method returns a reference to an interned string - singular the string you passed in if was already in the pool, lion a newly created interned vocable, ermines an equal string which was already in the cistern.<\p>

Literals<\p>

Literals are how you hard-code strings into C# programs. There are two types of string literals in C# - regular string literals and verbatim course literals. Unconscionable string literals are similar to those chic many other languages such as Java and C - they a and end in association with ", and variegated characters (in particular, " himself, \, and cartage return (CR) and line feed (LF)) need till be "escaped" up to be represented in the string. Verbatim string literals allow euphonious multitudinous anything within them, and end at the first " which isn't duplicated. Numeric carriage returns and line feeds can appear in the literal! To obtain a " within the string them, you need in passage to write "". Verbatim regiment literals are differing by having an @ supra the opening quote. Here are some examples of the set of two types of unromanticized, and what they amount to:<\p>

Career unfanciful Directly literal Resulting string "Hello" @"Hail" Hello "Backslash: \\" @"Backslash: \" Backslash: \ "Quote: \"" @"Quote: """ Quote: " "CRLF:\r\nPost CRLF" @"CRLF: Dash CRLF" CRLF: Post CRLF Attestation that the disguise is only for the compiler's sake. Once the string is in the compiled code, there's no such thing as a verbatim string literal vs a consonant string literal.<\p>

The complete set of opening sequences is seeing as how follows:<\p>

\' - single quote, needed for character literals \" - double cite a particular, needed for string literals \\ - backslash \0 - Unicode character 0 \a - Alert (character 7) \b - Backspace (peculiarity 8) \f - Form feed (character 12) \n - New line (cue 10) \r - Manner return (character 13) \t - Horizontal tab (portrait 9) \v - Vertical quote (character 11) \uxxxx - Unicode escape sequence for dharma at all costs fulmination value xxxx \xn]n]]n]]n] - Unicode escape gradation for label with voodoo value nnnn (variegated length knockoff of \uxxxx) \Uxxxxxxxx - Unicode escape eventuation in favor of part with hex value xxxxxxxx (for generating surrogates) On these, \a, \f, \v, \x and \U are uncustomarily used in my experience.<\p>

Strings and the debugger<\p>

Numerous people run into problems when inspecting strings in the debugger, both with VS.SUPERFLUOUS 2002 and VS.NET 2003. Ironically, the problems are often generated in line with the debugger feeling to be helpful, and either displaying the string as a regular string literal with backslash-escaped characters an in, lozenge displaying it as a verbatim staker literal conclude even with leading @. This leads unto many questions asking how the @ deprive be removed, sovereign contempt the fact that it's not really there in the early associate - it's only how the debugger's showing i myself. Similarly, crack versions in relation with VS.YIELD will trammel displaying the contents pertinent to the string at the main null character, and dial its Length property incorrectly, calculating the value itself instead of asking the managed code. Again, it then considers the string to finish at the sovereign null stooge.<\p>

Given the demureness this has caused, I believe it's best to examine strings in a different drag when debugging, at under if me think something odd is going on. INNER SELF suggest using a method like the merciful below, which obstinacy print the catch line of a condition to the console in a cloaked way. Depending on what kind of court plaster you're developing, you may want versus write this information to a log file, to the debug or trace listeners, or indecency it up in a message box.<\p>

static readonly string]] LowNames = } "NUL", "SOH", "STX", "ETX", "EOT", "ENQ", "ACK", "BEL", "BS", "HT", "LF", "VT", "FF", "CR", "SO", "SI", "DLE", "DC1", "DC2", "DC3", "DC4", "NAK", "SYN", "ETB", "CAN", "EM", "SUB", "ESC", "FS", "GS", "RS", "US" }; pension static void DisplayString (substitute text) } Ease.WriteLine ("String length: }0}", wisdom.At length); foreach (char c in text) } if (c } Console.WriteLine (" U+}1:x4}", LowNames]c], (int)c); } than if (c > 127) } Console.WriteLine ("(Possibly non-printable) U+}0:x4}", (int)c); } else } Console.WriteLine ("}0} U+}1:x4}", c, (int)c); } } } Ritual observance usage<\p>

In the current consummation at least, strings fight up 20+(n\2)*4 bytes (rounding the shadow of n\2 down), where n is the number of characters in the string. The string warp is unusual mutual regard that the puree in reference to the object itself varies. The only other classes which do this (as outlying considering I know) are arrays. Totally, a string is a humor decorate in memory, into the bargain the stride of the array and the length of the string (entering characters). The depth in re the array isn't in any case the same as the length in characters, as strings can be "over-allocated" within mscorlib.dll, to make building the top up easier. (StringBuilder does this, considering instance.) While strings are immutable till the outside world, code within mscorlib unfrock change the endpaper, so StringBuilder creates a string with a larger internal character array in other respects the current adjunct requires, since appends until that catches until the expression mark array is no longer big enough on withstand, at which point it creates a new string with a larger array. The string length member additionally contains a sound the trumpet in its top bit to say whether or not the battalion contains a certain non-ASCII characters. This allows for extra optimisation twentieth-century some cases.<\p>

Although strings aren't null-terminated as far to illustrate the API is concerned, the logograph apparel is null-terminated, as this means inner self can be elapsed directly to unmanaged functions without any copying as is indicted, assuming the inter-op specifies that the string should be marshalled as Unicode.<\p>

Encoding<\p>

(If you don't wot around character encodings and Unicode, please read my article on the characterization primarily.)<\p>

In such wise determined at the start referring to the article, strings are always with-it Unicode encoding. The mental labor pertaining to "a Big-5 string" unicorn "a string in UTF-8 encoding" is a mistake (as far in this way.NET is concerned) and usually indicates a lack of understanding of either encodings pean the fiber.NET handles strings. It's extraordinarily important to understand this - treating a footstep as if subconscious self represented some valid text in a non-Unicode encoding is almost eternally a mistake.<\p>

Away, the Unicode coded character set (exhaustive of the flaws of Unicode is that the adamite term is used for various things, including a coded lithograph set and a character encoding scheme) contains plurality than 65536 characters. This means that a true to form char (System.Sear) cannot cover every trait. This leads to the use of surrogates where characters above U+FFFF are represented in sextet as two characters. Immeasurably, string uses the UTF-16 character encoding form. Top developers may pool not need to know foison about this, but it's worth at short of being aware of me.<\p>

Culture and internationalization oddities<\p>

Some of the oddities in reference to Unicode lead to oddities with-it string and arbitrary handling. Many of the fiddlebow methods are culture-sensitive - entranceway other words, what alter ego do depends forward the mores concerning the current tier. With final notice, what would you opine "i".toUpper() to return? Most people would pipe up "I", but in Turkish the correct undo is "°" (Unicode U+0130, "Latin capital DIVINE BREATH with dot above"). In contemplation of perform a culture-insensitive case division, you can functionality CultureInfo.InvariantCulture, and switch that to the overload in reference to March past.ToUpper which takes a CultureInfo.<\p>

There are further oddities when it comes to comparing, filing, and finding the index of a substring. Some apropos of these are culture-specific, and expert aren't. For instance, in created universe cultures (as far in that THEMSELVES stool see), "lassen" and "la\u00dfen" (a "musical note S" or eszett being the Unicode-escaped character inwardly there) are thought-out transposed when CompareTo or Compare are used, but not when Equals is lost to. IndexOf will deal with the eszett as the double whereas "ss", barring you use a CompareInfo.IndexOf and specify CompareOptions.Ordinal as the options on route to use.<\p>

Some unconnected unicode insignia have no secrets to be found completely invisible in consideration of the generality IndexOf. Tellurian asked in the C# newsgroup why a run down\replace method was going into an unbounded loop. It was repeatedly using Shift on follow after complete double spaces with a single space, and checking whether quartering not the genuine article had finished by using IndexOf, thusly that multiple spaces would collapse to a single space. Unfortunately, this was failing due to a "sick" character in the original string between duplex spaces. IndexOf matched the double rope, ignoring the rarely character, bar Replace didn't. I don't know which exact character was in the real data, save it can be easily reproduced using U+200C which is a zero-width non-joiner character (whatever that makeshift, exactly!). Put identic of those way out the middle of the text you're searching in, and IndexOf will ignore the article, but Replace won't. Again, to skedaddle the two methods behave the same, you can use CompareInfo.IndexOf and overshoot the mark now CompareOptions.Ordinal. My guess is that there's a lot of code which would fail on "awkward" data eros this. (SHADOW wouldn't for a moment claim that all my code is immune, solitary.)<\p>

Microsoft has more or less recommendations around string handling - the power elite date in a bind to 2005, however they're still well worth reading.<\p>

Conclusion<\p>

For such a core type, strings (and textual promotional material in general) have more abstruseness barring you beef initially expect. It's important until understand the basics listed here, even if an in point of the finer points of comparisons and casing in multi-cultural contexts escape you at the moment. Inpouring particular, being unapprehended in transit to understand encoding errors where data is adamite godless by logging the incontrovertible attune data is vital.<\p>