Does C# have something like PHP's mb_convert_e

Is there a way on C# that I can convert unicode strings into ASCII + html entities, and then back again? See, in PHP, I can do it like so:

<?php
// RUN ME AT COMMAND LINE
$sUnicode = '<b>Jöhan Strauß</b>';
echo "UNICODE: $sUnicode\n";
$sASCII = mb_convert_encoding($sUnicode, 'HTML-ENTITIES','UTF-8');
echo "ASCII: $sASCII\n";
$sUnicode = mb_convert_encoding($sASCII, 'UTF-8', 'HTML-ENTITIES');
echo "UNICODE (TRANSLATED BACK): $sUnicode\n";

Background:

I need this to work in C# .NET 2 because we are constrained and can't use a higher .NET library in an older application.
I handle the PHP backend on this application. I wanted to share some tips with the C# frontend team on this project.

回答1:

Yes, there's Encoding.Convert, although I rarely use it myself:

string text = "<b>Jöhan Strauß</b>";
byte[] ascii = Encoding.ASCII.GetBytes(text);
byte[] utf8 = Encoding.Convert(Encoding.ASCII, Encoding.UTF8, ascii);

I rarely find I want to convert from one encoded form to another - it's much more common to perform a one way conversion from text to binary (Encoding.GetBytes) or vice versa (Encoding.GetString).

回答2:

HTML-ENTITIES isn't really a character encoding even though the PHP API might hint so. <b>Jöhan Strauß</b> is still UTF-8 encoded text (or even ASCII, ISO-8859-1, pretty much anything).

I couldn't find anything premade, except html encoding functions which are not the same thing at all since they encode &, < etc while mb_convert_encoding doesn't. I made t his class that should work:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace ConsoleApplication6
{
    class HtmlEntities
    {


        private static Dictionary<string, int> EntitiesToCodePoints;
        private static Dictionary<int, string> CodePointsToEntities;

        private static void Init()
        {
            if (EntitiesToCodePoints == null || CodePointsToEntities == null)
            {
                EntitiesToCodePoints = new Dictionary<string, int>();
                CodePointsToEntities = new Dictionary<int, string>();

                EntitiesToCodePoints["nbsp"] = 160; EntitiesToCodePoints["iexcl"] = 161; EntitiesToCodePoints["cent"] = 162; EntitiesToCodePoints["pound"] = 163; EntitiesToCodePoints["curren"] = 164; EntitiesToCodePoints["yen"] = 165; EntitiesToCodePoints["brvbar"] = 166; EntitiesToCodePoints["sect"] = 167; EntitiesToCodePoints["uml"] = 168; EntitiesToCodePoints["copy"] = 169; EntitiesToCodePoints["ordf"] = 170; EntitiesToCodePoints["laquo"] = 171; EntitiesToCodePoints["not"] = 172; EntitiesToCodePoints["shy"] = 173; EntitiesToCodePoints["reg"] = 174; EntitiesToCodePoints["macr"] = 175; EntitiesToCodePoints["deg"] = 176; EntitiesToCodePoints["plusmn"] = 177; EntitiesToCodePoints["sup2"] = 178; EntitiesToCodePoints["sup3"] = 179; EntitiesToCodePoints["acute"] = 180; EntitiesToCodePoints["micro"] = 181; EntitiesToCodePoints["para"] = 182; EntitiesToCodePoints["middot"] = 183; EntitiesToCodePoints["cedil"] = 184; EntitiesToCodePoints["sup1"] = 185; EntitiesToCodePoints["ordm"] = 186; EntitiesToCodePoints["raquo"] = 187; EntitiesToCodePoints["frac14"] = 188; EntitiesToCodePoints["frac12"] = 189; EntitiesToCodePoints["frac34"] = 190; EntitiesToCodePoints["iquest"] = 191; EntitiesToCodePoints["Agrave"] = 192; EntitiesToCodePoints["Aacute"] = 193; EntitiesToCodePoints["Acirc"] = 194; EntitiesToCodePoints["Atilde"] = 195; EntitiesToCodePoints["Auml"] = 196; EntitiesToCodePoints["Aring"] = 197; EntitiesToCodePoints["AElig"] = 198; EntitiesToCodePoints["Ccedil"] = 199; EntitiesToCodePoints["Egrave"] = 200; EntitiesToCodePoints["Eacute"] = 201; EntitiesToCodePoints["Ecirc"] = 202; EntitiesToCodePoints["Euml"] = 203; EntitiesToCodePoints["Igrave"] = 204; EntitiesToCodePoints["Iacute"] = 205; EntitiesToCodePoints["Icirc"] = 206; EntitiesToCodePoints["Iuml"] = 207; EntitiesToCodePoints["ETH"] = 208; EntitiesToCodePoints["Ntilde"] = 209; EntitiesToCodePoints["Ograve"] = 210; EntitiesToCodePoints["Oacute"] = 211; EntitiesToCodePoints["Ocirc"] = 212; EntitiesToCodePoints["Otilde"] = 213; EntitiesToCodePoints["Ouml"] = 214; EntitiesToCodePoints["times"] = 215; EntitiesToCodePoints["Oslash"] = 216; EntitiesToCodePoints["Ugrave"] = 217; EntitiesToCodePoints["Uacute"] = 218; EntitiesToCodePoints["Ucirc"] = 219; EntitiesToCodePoints["Uuml"] = 220; EntitiesToCodePoints["Yacute"] = 221; EntitiesToCodePoints["THORN"] = 222; EntitiesToCodePoints["szlig"] = 223; EntitiesToCodePoints["agrave"] = 224; EntitiesToCodePoints["aacute"] = 225; EntitiesToCodePoints["acirc"] = 226; EntitiesToCodePoints["atilde"] = 227; EntitiesToCodePoints["auml"] = 228; EntitiesToCodePoints["aring"] = 229; EntitiesToCodePoints["aelig"] = 230; EntitiesToCodePoints["ccedil"] = 231; EntitiesToCodePoints["egrave"] = 232; EntitiesToCodePoints["eacute"] = 233; EntitiesToCodePoints["ecirc"] = 234; EntitiesToCodePoints["euml"] = 235; EntitiesToCodePoints["igrave"] = 236; EntitiesToCodePoints["iacute"] = 237; EntitiesToCodePoints["icirc"] = 238; EntitiesToCodePoints["iuml"] = 239; EntitiesToCodePoints["eth"] = 240; EntitiesToCodePoints["ntilde"] = 241; EntitiesToCodePoints["ograve"] = 242; EntitiesToCodePoints["oacute"] = 243; EntitiesToCodePoints["ocirc"] = 244; EntitiesToCodePoints["otilde"] = 245; EntitiesToCodePoints["ouml"] = 246; EntitiesToCodePoints["divide"] = 247; EntitiesToCodePoints["oslash"] = 248; EntitiesToCodePoints["ugrave"] = 249; EntitiesToCodePoints["uacute"] = 250; EntitiesToCodePoints["ucirc"] = 251; EntitiesToCodePoints["uuml"] = 252; EntitiesToCodePoints["yacute"] = 253; EntitiesToCodePoints["thorn"] = 254; EntitiesToCodePoints["yuml"] = 255; EntitiesToCodePoints["OElig"] = 338; EntitiesToCodePoints["oelig"] = 339; EntitiesToCodePoints["Scaron"] = 352; EntitiesToCodePoints["scaron"] = 353; EntitiesToCodePoints["Yuml"] = 376; EntitiesToCodePoints["fnof"] = 402; EntitiesToCodePoints["circ"] = 710; EntitiesToCodePoints["tilde"] = 732; EntitiesToCodePoints["Alpha"] = 913; EntitiesToCodePoints["Beta"] = 914; EntitiesToCodePoints["Gamma"] = 915; EntitiesToCodePoints["Delta"] = 916; EntitiesToCodePoints["Epsilon"] = 917; EntitiesToCodePoints["Zeta"] = 918; EntitiesToCodePoints["Eta"] = 919; EntitiesToCodePoints["Theta"] = 920; EntitiesToCodePoints["Iota"] = 921; EntitiesToCodePoints["Kappa"] = 922; EntitiesToCodePoints["Lambda"] = 923; EntitiesToCodePoints["Mu"] = 924; EntitiesToCodePoints["Nu"] = 925; EntitiesToCodePoints["Xi"] = 926; EntitiesToCodePoints["Omicron"] = 927; EntitiesToCodePoints["Pi"] = 928; EntitiesToCodePoints["Rho"] = 929; EntitiesToCodePoints["Sigma"] = 931; EntitiesToCodePoints["Tau"] = 932; EntitiesToCodePoints["Upsilon"] = 933; EntitiesToCodePoints["Phi"] = 934; EntitiesToCodePoints["Chi"] = 935; EntitiesToCodePoints["Psi"] = 936; EntitiesToCodePoints["Omega"] = 937; EntitiesToCodePoints["alpha"] = 945; EntitiesToCodePoints["beta"] = 946; EntitiesToCodePoints["gamma"] = 947; EntitiesToCodePoints["delta"] = 948; EntitiesToCodePoints["epsilon"] = 949; EntitiesToCodePoints["zeta"] = 950; EntitiesToCodePoints["eta"] = 951; EntitiesToCodePoints["theta"] = 952; EntitiesToCodePoints["iota"] = 953; EntitiesToCodePoints["kappa"] = 954; EntitiesToCodePoints["lambda"] = 955; EntitiesToCodePoints["mu"] = 956; EntitiesToCodePoints["nu"] = 957; EntitiesToCodePoints["xi"] = 958; EntitiesToCodePoints["omicron"] = 959; EntitiesToCodePoints["pi"] = 960; EntitiesToCodePoints["rho"] = 961; EntitiesToCodePoints["sigmaf"] = 962; EntitiesToCodePoints["sigma"] = 963; EntitiesToCodePoints["tau"] = 964; EntitiesToCodePoints["upsilon"] = 965; EntitiesToCodePoints["phi"] = 966; EntitiesToCodePoints["chi"] = 967; EntitiesToCodePoints["psi"] = 968; EntitiesToCodePoints["omega"] = 969; EntitiesToCodePoints["thetasym"] = 977; EntitiesToCodePoints["upsih"] = 978; EntitiesToCodePoints["piv"] = 982; EntitiesToCodePoints["ensp"] = 8194; EntitiesToCodePoints["emsp"] = 8195; EntitiesToCodePoints["thinsp"] = 8201; EntitiesToCodePoints["zwnj"] = 8204; EntitiesToCodePoints["zwj"] = 8205; EntitiesToCodePoints["lrm"] = 8206; EntitiesToCodePoints["rlm"] = 8207; EntitiesToCodePoints["ndash"] = 8211; EntitiesToCodePoints["mdash"] = 8212; EntitiesToCodePoints["lsquo"] = 8216; EntitiesToCodePoints["rsquo"] = 8217; EntitiesToCodePoints["sbquo"] = 8218; EntitiesToCodePoints["ldquo"] = 8220; EntitiesToCodePoints["rdquo"] = 8221; EntitiesToCodePoints["bdquo"] = 8222; EntitiesToCodePoints["dagger"] = 8224; EntitiesToCodePoints["Dagger"] = 8225; EntitiesToCodePoints["bull"] = 8226; EntitiesToCodePoints["hellip"] = 8230; EntitiesToCodePoints["permil"] = 8240; EntitiesToCodePoints["prime"] = 8242; EntitiesToCodePoints["Prime"] = 8243; EntitiesToCodePoints["lsaquo"] = 8249; EntitiesToCodePoints["rsaquo"] = 8250; EntitiesToCodePoints["oline"] = 8254; EntitiesToCodePoints["frasl"] = 8260; EntitiesToCodePoints["euro"] = 8364; EntitiesToCodePoints["weierp"] = 8472; EntitiesToCodePoints["image"] = 8465; EntitiesToCodePoints["real"] = 8476; EntitiesToCodePoints["trade"] = 8482; EntitiesToCodePoints["alefsym"] = 8501; EntitiesToCodePoints["larr"] = 8592; EntitiesToCodePoints["uarr"] = 8593; EntitiesToCodePoints["rarr"] = 8594; EntitiesToCodePoints["darr"] = 8595; EntitiesToCodePoints["harr"] = 8596; EntitiesToCodePoints["crarr"] = 8629; EntitiesToCodePoints["lArr"] = 8656; EntitiesToCodePoints["uArr"] = 8657; EntitiesToCodePoints["rArr"] = 8658; EntitiesToCodePoints["dArr"] = 8659; EntitiesToCodePoints["hArr"] = 8660; EntitiesToCodePoints["forall"] = 8704; EntitiesToCodePoints["part"] = 8706; EntitiesToCodePoints["exist"] = 8707; EntitiesToCodePoints["empty"] = 8709; EntitiesToCodePoints["nabla"] = 8711; EntitiesToCodePoints["isin"] = 8712; EntitiesToCodePoints["notin"] = 8713; EntitiesToCodePoints["ni"] = 8715; EntitiesToCodePoints["prod"] = 8719; EntitiesToCodePoints["sum"] = 8721; EntitiesToCodePoints["minus"] = 8722; EntitiesToCodePoints["lowast"] = 8727; EntitiesToCodePoints["radic"] = 8730; EntitiesToCodePoints["prop"] = 8733; EntitiesToCodePoints["infin"] = 8734; EntitiesToCodePoints["ang"] = 8736; EntitiesToCodePoints["and"] = 8743; EntitiesToCodePoints["or"] = 8744; EntitiesToCodePoints["cap"] = 8745; EntitiesToCodePoints["cup"] = 8746; EntitiesToCodePoints["int"] = 8747; EntitiesToCodePoints["there4"] = 8756; EntitiesToCodePoints["sim"] = 8764; EntitiesToCodePoints["cong"] = 8773; EntitiesToCodePoints["asymp"] = 8776; EntitiesToCodePoints["ne"] = 8800; EntitiesToCodePoints["equiv"] = 8801; EntitiesToCodePoints["le"] = 8804; EntitiesToCodePoints["ge"] = 8805; EntitiesToCodePoints["sub"] = 8834; EntitiesToCodePoints["sup"] = 8835; EntitiesToCodePoints["nsub"] = 8836; EntitiesToCodePoints["sube"] = 8838; EntitiesToCodePoints["supe"] = 8839; EntitiesToCodePoints["oplus"] = 8853; EntitiesToCodePoints["otimes"] = 8855; EntitiesToCodePoints["perp"] = 8869; EntitiesToCodePoints["sdot"] = 8901; EntitiesToCodePoints["lceil"] = 8968; EntitiesToCodePoints["rceil"] = 8969; EntitiesToCodePoints["lfloor"] = 8970; EntitiesToCodePoints["rfloor"] = 8971; EntitiesToCodePoints["lang"] = 9001; EntitiesToCodePoints["rang"] = 9002; EntitiesToCodePoints["loz"] = 9674; EntitiesToCodePoints["spades"] = 9824; EntitiesToCodePoints["clubs"] = 9827; EntitiesToCodePoints["hearts"] = 9829; EntitiesToCodePoints["diams"] = 9830;
                CodePointsToEntities[160] = "nbsp"; CodePointsToEntities[161] = "iexcl"; CodePointsToEntities[162] = "cent"; CodePointsToEntities[163] = "pound"; CodePointsToEntities[164] = "curren"; CodePointsToEntities[165] = "yen"; CodePointsToEntities[166] = "brvbar"; CodePointsToEntities[167] = "sect"; CodePointsToEntities[168] = "uml"; CodePointsToEntities[169] = "copy"; CodePointsToEntities[170] = "ordf"; CodePointsToEntities[171] = "laquo"; CodePointsToEntities[172] = "not"; CodePointsToEntities[173] = "shy"; CodePointsToEntities[174] = "reg"; CodePointsToEntities[175] = "macr"; CodePointsToEntities[176] = "deg"; CodePointsToEntities[177] = "plusmn"; CodePointsToEntities[178] = "sup2"; CodePointsToEntities[179] = "sup3"; CodePointsToEntities[180] = "acute"; CodePointsToEntities[181] = "micro"; CodePointsToEntities[182] = "para"; CodePointsToEntities[183] = "middot"; CodePointsToEntities[184] = "cedil"; CodePointsToEntities[185] = "sup1"; CodePointsToEntities[186] = "ordm"; CodePointsToEntities[187] = "raquo"; CodePointsToEntities[188] = "frac14"; CodePointsToEntities[189] = "frac12"; CodePointsToEntities[190] = "frac34"; CodePointsToEntities[191] = "iquest"; CodePointsToEntities[192] = "Agrave"; CodePointsToEntities[193] = "Aacute"; CodePointsToEntities[194] = "Acirc"; CodePointsToEntities[195] = "Atilde"; CodePointsToEntities[196] = "Auml"; CodePointsToEntities[197] = "Aring"; CodePointsToEntities[198] = "AElig"; CodePointsToEntities[199] = "Ccedil"; CodePointsToEntities[200] = "Egrave"; CodePointsToEntities[201] = "Eacute"; CodePointsToEntities[202] = "Ecirc"; CodePointsToEntities[203] = "Euml"; CodePointsToEntities[204] = "Igrave"; CodePointsToEntities[205] = "Iacute"; CodePointsToEntities[206] = "Icirc"; CodePointsToEntities[207] = "Iuml"; CodePointsToEntities[208] = "ETH"; CodePointsToEntities[209] = "Ntilde"; CodePointsToEntities[210] = "Ograve"; CodePointsToEntities[211] = "Oacute"; CodePointsToEntities[212] = "Ocirc"; CodePointsToEntities[213] = "Otilde"; CodePointsToEntities[214] = "Ouml"; CodePointsToEntities[215] = "times"; CodePointsToEntities[216] = "Oslash"; CodePointsToEntities[217] = "Ugrave"; CodePointsToEntities[218] = "Uacute"; CodePointsToEntities[219] = "Ucirc"; CodePointsToEntities[220] = "Uuml"; CodePointsToEntities[221] = "Yacute"; CodePointsToEntities[222] = "THORN"; CodePointsToEntities[223] = "szlig"; CodePointsToEntities[224] = "agrave"; CodePointsToEntities[225] = "aacute"; CodePointsToEntities[226] = "acirc"; CodePointsToEntities[227] = "atilde"; CodePointsToEntities[228] = "auml"; CodePointsToEntities[229] = "aring"; CodePointsToEntities[230] = "aelig"; CodePointsToEntities[231] = "ccedil"; CodePointsToEntities[232] = "egrave"; CodePointsToEntities[233] = "eacute"; CodePointsToEntities[234] = "ecirc"; CodePointsToEntities[235] = "euml"; CodePointsToEntities[236] = "igrave"; CodePointsToEntities[237] = "iacute"; CodePointsToEntities[238] = "icirc"; CodePointsToEntities[239] = "iuml"; CodePointsToEntities[240] = "eth"; CodePointsToEntities[241] = "ntilde"; CodePointsToEntities[242] = "ograve"; CodePointsToEntities[243] = "oacute"; CodePointsToEntities[244] = "ocirc"; CodePointsToEntities[245] = "otilde"; CodePointsToEntities[246] = "ouml"; CodePointsToEntities[247] = "divide"; CodePointsToEntities[248] = "oslash"; CodePointsToEntities[249] = "ugrave"; CodePointsToEntities[250] = "uacute"; CodePointsToEntities[251] = "ucirc"; CodePointsToEntities[252] = "uuml"; CodePointsToEntities[253] = "yacute"; CodePointsToEntities[254] = "thorn"; CodePointsToEntities[255] = "yuml"; CodePointsToEntities[338] = "OElig"; CodePointsToEntities[339] = "oelig"; CodePointsToEntities[352] = "Scaron"; CodePointsToEntities[353] = "scaron"; CodePointsToEntities[376] = "Yuml"; CodePointsToEntities[402] = "fnof"; CodePointsToEntities[710] = "circ"; CodePointsToEntities[732] = "tilde"; CodePointsToEntities[913] = "Alpha"; CodePointsToEntities[914] = "Beta"; CodePointsToEntities[915] = "Gamma"; CodePointsToEntities[916] = "Delta"; CodePointsToEntities[917] = "Epsilon"; CodePointsToEntities[918] = "Zeta"; CodePointsToEntities[919] = "Eta"; CodePointsToEntities[920] = "Theta"; CodePointsToEntities[921] = "Iota"; CodePointsToEntities[922] = "Kappa"; CodePointsToEntities[923] = "Lambda"; CodePointsToEntities[924] = "Mu"; CodePointsToEntities[925] = "Nu"; CodePointsToEntities[926] = "Xi"; CodePointsToEntities[927] = "Omicron"; CodePointsToEntities[928] = "Pi"; CodePointsToEntities[929] = "Rho"; CodePointsToEntities[931] = "Sigma"; CodePointsToEntities[932] = "Tau"; CodePointsToEntities[933] = "Upsilon"; CodePointsToEntities[934] = "Phi"; CodePointsToEntities[935] = "Chi"; CodePointsToEntities[936] = "Psi"; CodePointsToEntities[937] = "Omega"; CodePointsToEntities[945] = "alpha"; CodePointsToEntities[946] = "beta"; CodePointsToEntities[947] = "gamma"; CodePointsToEntities[948] = "delta"; CodePointsToEntities[949] = "epsilon"; CodePointsToEntities[950] = "zeta"; CodePointsToEntities[951] = "eta"; CodePointsToEntities[952] = "theta"; CodePointsToEntities[953] = "iota"; CodePointsToEntities[954] = "kappa"; CodePointsToEntities[955] = "lambda"; CodePointsToEntities[956] = "mu"; CodePointsToEntities[957] = "nu"; CodePointsToEntities[958] = "xi"; CodePointsToEntities[959] = "omicron"; CodePointsToEntities[960] = "pi"; CodePointsToEntities[961] = "rho"; CodePointsToEntities[962] = "sigmaf"; CodePointsToEntities[963] = "sigma"; CodePointsToEntities[964] = "tau"; CodePointsToEntities[965] = "upsilon"; CodePointsToEntities[966] = "phi"; CodePointsToEntities[967] = "chi"; CodePointsToEntities[968] = "psi"; CodePointsToEntities[969] = "omega"; CodePointsToEntities[977] = "thetasym"; CodePointsToEntities[978] = "upsih"; CodePointsToEntities[982] = "piv"; CodePointsToEntities[8194] = "ensp"; CodePointsToEntities[8195] = "emsp"; CodePointsToEntities[8201] = "thinsp"; CodePointsToEntities[8204] = "zwnj"; CodePointsToEntities[8205] = "zwj"; CodePointsToEntities[8206] = "lrm"; CodePointsToEntities[8207] = "rlm"; CodePointsToEntities[8211] = "ndash"; CodePointsToEntities[8212] = "mdash"; CodePointsToEntities[8216] = "lsquo"; CodePointsToEntities[8217] = "rsquo"; CodePointsToEntities[8218] = "sbquo"; CodePointsToEntities[8220] = "ldquo"; CodePointsToEntities[8221] = "rdquo"; CodePointsToEntities[8222] = "bdquo"; CodePointsToEntities[8224] = "dagger"; CodePointsToEntities[8225] = "Dagger"; CodePointsToEntities[8226] = "bull"; CodePointsToEntities[8230] = "hellip"; CodePointsToEntities[8240] = "permil"; CodePointsToEntities[8242] = "prime"; CodePointsToEntities[8243] = "Prime"; CodePointsToEntities[8249] = "lsaquo"; CodePointsToEntities[8250] = "rsaquo"; CodePointsToEntities[8254] = "oline"; CodePointsToEntities[8260] = "frasl"; CodePointsToEntities[8364] = "euro"; CodePointsToEntities[8472] = "weierp"; CodePointsToEntities[8465] = "image"; CodePointsToEntities[8476] = "real"; CodePointsToEntities[8482] = "trade"; CodePointsToEntities[8501] = "alefsym"; CodePointsToEntities[8592] = "larr"; CodePointsToEntities[8593] = "uarr"; CodePointsToEntities[8594] = "rarr"; CodePointsToEntities[8595] = "darr"; CodePointsToEntities[8596] = "harr"; CodePointsToEntities[8629] = "crarr"; CodePointsToEntities[8656] = "lArr"; CodePointsToEntities[8657] = "uArr"; CodePointsToEntities[8658] = "rArr"; CodePointsToEntities[8659] = "dArr"; CodePointsToEntities[8660] = "hArr"; CodePointsToEntities[8704] = "forall"; CodePointsToEntities[8706] = "part"; CodePointsToEntities[8707] = "exist"; CodePointsToEntities[8709] = "empty"; CodePointsToEntities[8711] = "nabla"; CodePointsToEntities[8712] = "isin"; CodePointsToEntities[8713] = "notin"; CodePointsToEntities[8715] = "ni"; CodePointsToEntities[8719] = "prod"; CodePointsToEntities[8721] = "sum"; CodePointsToEntities[8722] = "minus"; CodePointsToEntities[8727] = "lowast"; CodePointsToEntities[8730] = "radic"; CodePointsToEntities[8733] = "prop"; CodePointsToEntities[8734] = "infin"; CodePointsToEntities[8736] = "ang"; CodePointsToEntities[8743] = "and"; CodePointsToEntities[8744] = "or"; CodePointsToEntities[8745] = "cap"; CodePointsToEntities[8746] = "cup"; CodePointsToEntities[8747] = "int"; CodePointsToEntities[8756] = "there4"; CodePointsToEntities[8764] = "sim"; CodePointsToEntities[8773] = "cong"; CodePointsToEntities[8776] = "asymp"; CodePointsToEntities[8800] = "ne"; CodePointsToEntities[8801] = "equiv"; CodePointsToEntities[8804] = "le"; CodePointsToEntities[8805] = "ge"; CodePointsToEntities[8834] = "sub"; CodePointsToEntities[8835] = "sup"; CodePointsToEntities[8836] = "nsub"; CodePointsToEntities[8838] = "sube"; CodePointsToEntities[8839] = "supe"; CodePointsToEntities[8853] = "oplus"; CodePointsToEntities[8855] = "otimes"; CodePointsToEntities[8869] = "perp"; CodePointsToEntities[8901] = "sdot"; CodePointsToEntities[8968] = "lceil"; CodePointsToEntities[8969] = "rceil"; CodePointsToEntities[8970] = "lfloor"; CodePointsToEntities[8971] = "rfloor"; CodePointsToEntities[9001] = "lang"; CodePointsToEntities[9002] = "rang"; CodePointsToEntities[9674] = "loz"; CodePointsToEntities[9824] = "spades"; CodePointsToEntities[9827] = "clubs"; CodePointsToEntities[9829] = "hearts"; CodePointsToEntities[9830] = "diams";

            }
        }

        public static string Decode(string str)
        {
            Init();
            return Regex.Replace(str, @"&(?:#(?<num>[0-9]+)|(?<named>[0-9A-Za-z]+));", delegate(Match m)
            {
                int charCode;
                string captured;
                if (m.Groups["num"].Captures.Count > 0)
                {

                    if (!int.TryParse(m.Groups["num"].ToString(), out charCode))
                    {//Return unaffected

                        return m.Groups[0].ToString();
                    }
                }
                else
                {
                    captured = m.Groups["named"].ToString();
                    if( EntitiesToCodePoints.ContainsKey(captured) ) {
                        charCode = EntitiesToCodePoints[captured];
                    }
                    else {
                        //Return unaffected

                        return m.Groups[0].ToString();
                    }
                }
                return Convert.ToChar(charCode).ToString();
            });
        }

        public static string Encode(string str)
        {
            Init();
            return Regex.Replace(str, @"[\u0080-\uDAFF\uE000-\uFFFF]", delegate(Match m)
            {
                int codePoint = (int)m.Value[0];
                if (CodePointsToEntities.ContainsKey(codePoint))
                {
                    return "&" + CodePointsToEntities[codePoint] + ";";
                }
                return "&#" + codePoint + ";";
            });
        }
    }
}

PHP:

$a = "ɢ♠♤ä<>&'\"";
$b = mb_convert_encoding( $a, "HTML-ENTITIES", "UTF-8" );
echo $b; //&#610;&spades;&#9828;&auml;<>&'"
echo mb_convert_encoding( $b, "UTF-8", "HTML-ENTITIES"); //ɢ♠♤ä<>&'"

string a = "ɢ♠♤ä<>&'\"";
string b = HtmlEntities.Encode(a);
Console.WriteLine(b); //&#610;&spades;&#9828;&auml;<>&'"
Console.WriteLine(HtmlEntities.Decode(b)); //ɢ♠♤ä<>&'"

Note: This cannot handle characters outside BMP, though such a requirement is so rare that it should be explicitly mentioned.

回答3:

Here are some examples of conversions. The first two show how to convert, the last one can be turned into a function that takes two encoding names as strings, and convert.

A list of encoding names can be found here.

Encoding.UTF8.GetString(Encoding.ASCII.GetBytes(str));
Encoding.UTF8.GetString(Encoding.Unicode.GetBytes(str));
Encoding.GetEncoding("UTF-8").GetString(Encoding.GetEncoding("ASCII").GetBytes(str));