之前在面試話題中介紹了如何言簡意赅的回答各種char的使用差別，本文将談到另外一個高頻問題——codepage跟charset的差別和聯系。雖然這兩個概念幾乎天天都會在工作中出現，但就個人過往經驗看，面對該問題時能夠給出清晰答案的着實鳳毛麟角。
首先來看codepage（“内碼表”或者“代碼頁”），這是wiki對他的定義——代碼頁是字元編碼的别名，也稱“内碼表”，是特定語言的字元集的一張表。（https://zh.wikipedia.org/wiki/%E4%BB%A3%E7%A0%81%E9%A1%B5）
那麼對于字元編碼，wiki又是什麼如何定義的？字元編碼（英語：Characterencoding）、字集碼是把字元集中的字元編碼為指定集合中某一對象（例如：比特模式、自然數序列、8位組或者電脈沖），以便文本在計算機中存儲和通過通信網絡的傳遞。按照慣例，人們認為字元集和字元編碼是同義詞，因為使用同樣的标準來定義提供什麼字元并且這些字元如何編碼到一系列的代碼單元（通常一個字元一個單元）。（https://zh.wikipedia.org/wiki/%E5%AD%97%E7%AC%A6%E7%BC%96%E7%A0%81）
搞了半天原來這二者是同義詞啊，也就是大名跟小名的關系呗！是以Code Page 936 就是GB2312，Code Page 950 就是BIG5，而Code Page 65001就對應UTF-8。這就破哏了？文章可以結束了吧？如果故事就這麼簡單，那還真是很傻很天真……
盡管這二者在很多情況下是同義詞，但在web開發中兩者的作用域還是明顯不同的。這裡我們将以ASP.NET為技術背景，來進行進一步剖析。首先new一個WebForm工程，在default page中添加如下代碼：
namespace CodepageTest
{
public partial class _Default : Page
{
protected void Page_Load(object sender,EventArgs e)
{
Response.Write("Codepage is :" + Session.CodePage.ToString());
}
}
}
啟動程式，我們可以看到如下内容。
一切正常！檢視header，發現charset已設定為utf-8。
修改代碼，添加Session.CodePage = 950; 後再次運作，亂碼出現了。
responds header中的charset也随之顯示為big5。
到這步已經有人開始提示我說，在浏覽中點選檢視->編碼，然後選擇UTF-8不就好了麼？OK! 如你所願。選擇完畢後，page顯示如下圖。
到這裡我們其實已經發現，在ASP.NET中codepage的作用域在伺服器端，而charset的作用域在浏覽器端，兩者的最大差別就在于此。同時他們必須比對，才能有效避免亂碼問題的出現，任何一方的單獨行動都于事無補。
最後附上codepage和charset的對應關系表，熟記其中的幾個常用對應關系，無論對于工作還是面試相信都大有裨益。
| CodePage | CharSet | Display Name |
| 37 | IBM037 | IBM EBCDIC (US-Canada) |
| 437 | IBM437 | OEM United States |
| 500 | IBM500 | IBM EBCDIC (International) |
| 708 | ASMO-708 | Arabic (ASMO 708) |
| 720 | DOS-720 | Arabic (DOS) |
| 737 | ibm737 | Greek (DOS) |
| 775 | ibm775 | Baltic (DOS) |
| 850 | ibm850 | Western European (DOS) |
| 852 | ibm852 | Central European (DOS) |
| 855 | IBM855 | OEM Cyrillic |
| 857 | ibm857 | Turkish (DOS) |
| 858 | IBM00858 | OEM Multilingual Latin I |
| 860 | IBM860 | Portuguese (DOS) |
| 861 | ibm861 | Icelandic (DOS) |
| 862 | DOS-862 | Hebrew (DOS) |
| 863 | IBM863 | French Canadian (DOS) |
| 864 | IBM864 | Arabic (864) |
| 865 | IBM865 | Nordic (DOS) |
| 866 | cp866 | Cyrillic (DOS) |
| 869 | ibm869 | Greek, Modern (DOS) |
| 870 | IBM870 | IBM EBCDIC (Multilingual Latin-2) |
| 874 | windows-874 | Thai (Windows) |
| 875 | cp875 | IBM EBCDIC (Greek Modern) |
| 932 | shift_jis | Japanese (Shift-JIS) |
| 936 | gb2312 | Chinese Simplified (GB2312) |
| 949 | ks_c_5601-1987 | Korean |
| 950 | big5 | Chinese Traditional (Big5) |
| 1026 | IBM1026 | IBM EBCDIC (Turkish Latin-5) |
| 1047 | IBM01047 | IBM Latin-1 |
| 1140 | IBM01140 | IBM EBCDIC (US-Canada-Euro) |
| 1141 | IBM01141 | IBM EBCDIC (Germany-Euro) |
| 1142 | IBM01142 | IBM EBCDIC (Denmark-Norway-Euro) |
| 1143 | IBM01143 | IBM EBCDIC (Finland-Sweden-Euro) |
| 1144 | IBM01144 | IBM EBCDIC (Italy-Euro) |
| 1145 | IBM01145 | IBM EBCDIC (Spain-Euro) |
| 1146 | IBM01146 | IBM EBCDIC (UK-Euro) |
| 1147 | IBM01147 | IBM EBCDIC (France-Euro) |
| 1148 | IBM01148 | IBM EBCDIC (International-Euro) |
| 1149 | IBM01149 | IBM EBCDIC (Icelandic-Euro) |
| 1200 | utf-16 | Unicode |
| 1201 | UnicodeFFFE | Unicode (Big-Endian) |
| 1250 | windows-1250 | Central European (Windows) |
| 1251 | windows-1251 | Cyrillic (Windows) |
| 1252 | Windows-1252 | Western European (Windows) |
| 1253 | windows-1253 | Greek (Windows) |
| 1254 | windows-1254 | Turkish (Windows) |
| 1255 | windows-1255 | Hebrew (Windows) |
| 1256 | windows-1256 | Arabic (Windows) |
| 1257 | windows-1257 | Baltic (Windows) |
| 1258 | windows-1258 | Vietnamese (Windows) |
| 1361 | Johab | Korean (Johab) |
| 10000 | macintosh | Western European (Mac) |
| 10001 | x-mac-japanese | Japanese (Mac) |
| 10002 | x-mac-chinesetrad | Chinese Traditional (Mac) |
| 10003 | x-mac-korean | Korean (Mac) |
| 10004 | x-mac-arabic | Arabic (Mac) |
| 10005 | x-mac-hebrew | Hebrew (Mac) |
| 10006 | x-mac-greek | Greek (Mac) |
| 10007 | x-mac-cyrillic | Cyrillic (Mac) |
| 10008 | x-mac-chinesesimp | Chinese Simplified (Mac) |
| 10010 | x-mac-romanian | Romanian (Mac) |
| 10017 | x-mac-ukrainian | Ukrainian (Mac) |
| 10021 | x-mac-thai | Thai (Mac) |
| 10029 | x-mac-ce | Central European (Mac) |
| 10079 | x-mac-icelandic | Icelandic (Mac) |
| 10081 | x-mac-turkish | Turkish (Mac) |
| 10082 | x-mac-croatian | Croatian (Mac) |
| 20000 | x-Chinese-CNS | Chinese Traditional (CNS) |
| 20001 | x-cp20001 | TCA Taiwan |
| 20002 | x-Chinese-Eten | Chinese Traditional (Eten) |
| 20003 | x-cp20003 | IBM5550 Taiwan |
| 20004 | x-cp20004 | TeleText Taiwan |
| 20005 | x-cp20005 | Wang Taiwan |
| 20105 | x-IA5 | Western European (IA5) |
| 20106 | x-IA5-German | German (IA5) |
| 20107 | x-IA5-Swedish | Swedish (IA5) |
| 20108 | x-IA5-Norwegian | Norwegian (IA5) |
| 20127 | us-ascii | US-ASCII |
| 20261 | x-cp20261 | T.61 |
| 20269 | x-cp20269 | ISO-6937 |
| 20273 | IBM273 | IBM EBCDIC (Germany) |
| 20277 | IBM277 | IBM EBCDIC (Denmark-Norway) |
| 20278 | IBM278 | IBM EBCDIC (Finland-Sweden) |
| 20280 | IBM280 | IBM EBCDIC (Italy) |
| 20284 | IBM284 | IBM EBCDIC (Spain) |
| 20285 | IBM285 | IBM EBCDIC (UK) |
| 20290 | IBM290 | IBM EBCDIC (Japanese katakana) |
| 20297 | IBM297 | IBM EBCDIC (France) |
| 20420 | IBM420 | IBM EBCDIC (Arabic) |
| 20423 | IBM423 | IBM EBCDIC (Greek) |
| 20424 | IBM424 | IBM EBCDIC (Hebrew) |
| 20833 | x-EBCDIC-KoreanExtended | IBM EBCDIC (Korean Extended) |
| 20838 | IBM-Thai | IBM EBCDIC (Thai) |
| 20866 | koi8-r | Cyrillic (KOI8-R) |
| 20871 | IBM871 | IBM EBCDIC (Icelandic) |
| 20880 | IBM880 | IBM EBCDIC (Cyrillic Russian) |
| 20905 | IBM905 | IBM EBCDIC (Turkish) |
| 20924 | IBM00924 | IBM Latin-1 |
| 20932 | EUC-JP | Japanese (JIS 0208-1990 and 0212-1990) |
| 20936 | x-cp20936 | Chinese Simplified (GB2312-80) |
| 20949 | x-cp20949 | Korean Wansung |
| 21025 | cp1025 | IBM EBCDIC (Cyrillic Serbian-Bulgarian) |
| 21866 | koi8-u | Cyrillic (KOI8-U) |
| 28591 | iso-8859-1 | Western European (ISO) |
| 28592 | iso-8859-2 | Central European (ISO) |
| 28593 | iso-8859-3 | Latin 3 (ISO) |
| 28594 | iso-8859-4 | Baltic (ISO) |
| 28595 | iso-8859-5 | Cyrillic (ISO) |
| 28596 | iso-8859-6 | Arabic (ISO) |
| 28597 | iso-8859-7 | Greek (ISO) |
| 28598 | iso-8859-8 | Hebrew (ISO-Visual) |
| 28599 | iso-8859-9 | Turkish (ISO) |
| 28603 | iso-8859-13 | Estonian (ISO) |
| 28605 | iso-8859-15 | Latin 9 (ISO) |
| 29001 | x-Europa | Europa |
| 38598 | iso-8859-8-i | Hebrew (ISO-Logical) |
| 50220 | iso-2022-jp | Japanese (JIS) |
| 50221 | csISO2022JP | Japanese (JIS-Allow 1 byte Kana) |
| 50222 | iso-2022-jp | Japanese (JIS-Allow 1 byte Kana - SO/SI) |
| 50225 | iso-2022-kr | Korean (ISO) |
| 50227 | x-cp50227 | Chinese Simplified (ISO-2022) |
| 51932 | euc-jp | Japanese (EUC) |
| 51936 | EUC-CN | Chinese Simplified (EUC) |
| 51949 | euc-kr | Korean (EUC) |
| 52936 | hz-gb-2312 | Chinese Simplified (HZ) |
| 54936 | GB18030 | Chinese Simplified (GB18030) |
| 57002 | x-iscii-de | ISCII Devanagari |
| 57003 | x-iscii-be | ISCII Bengali |
| 57004 | x-iscii-ta | ISCII Tamil |
| 57005 | x-iscii-te | ISCII Telugu |
| 57006 | x-iscii-as | ISCII Assamese |
| 57007 | x-iscii-or | ISCII Oriya |
| 57008 | x-iscii-ka | ISCII Kannada |
| 57009 | x-iscii-ma | ISCII Malayalam |
| 57010 | x-iscii-gu | ISCII Gujarati |
| 57011 | x-iscii-pa | ISCII Punjabi |
| 65000 | utf-7 | Unicode (UTF-7) |
| 65001 | utf-8 | Unicode (UTF-8) |
| 65005 | utf-32 | Unicode (UTF-32) |
| 65006 | utf-32BE | Unicode (UTF-32 Big-Endian) |
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