NSStringEncoding enc = CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);NSString *retStr = [[NSString alloc] initWithData:data encoding:enc];
附：编码集列表
CFStringEncoding constants for encodings that may be supported by CFString.
enum {
kCFStringEncodingMacRoman = 0L,
kCFStringEncodingMacJapanese = 1,
kCFStringEncodingMacChineseTrad = 2,
kCFStringEncodingMacKorean = 3,
kCFStringEncodingMacArabic = 4,
kCFStringEncodingMacHebrew = 5,
kCFStringEncodingMacGreek = 6,
kCFStringEncodingMacCyrillic = 7,
kCFStringEncodingMacDevanagari = 9,
kCFStringEncodingMacGurmukhi = 10,
kCFStringEncodingMacGujarati = 11,
kCFStringEncodingMacOriya = 12,
kCFStringEncodingMacBengali = 13,
kCFStringEncodingMacTamil = 14,
kCFStringEncodingMacTelugu = 15,
kCFStringEncodingMacKannada = 16,
kCFStringEncodingMacMalayalam = 17,
kCFStringEncodingMacSinhalese = 18,
kCFStringEncodingMacBurmese = 19,
kCFStringEncodingMacKhmer = 20,
kCFStringEncodingMacThai = 21,
kCFStringEncodingMacLaotian = 22,
kCFStringEncodingMacGeorgian = 23,
kCFStringEncodingMacArmenian = 24,
kCFStringEncodingMacChineseSimp = 25,
kCFStringEncodingMacTibetan = 26,
kCFStringEncodingMacMongolian = 27,
kCFStringEncodingMacEthiopic = 28,
kCFStringEncodingMacCentralEurRoman = 29,
kCFStringEncodingMacVietnamese = 30,
kCFStringEncodingMacExtArabic = 31,
kCFStringEncodingMacSymbol = 33,
kCFStringEncodingMacDingbats = 34,
kCFStringEncodingMacTurkish = 35,
kCFStringEncodingMacCroatian = 36,
kCFStringEncodingMacIcelandic = 37,
kCFStringEncodingMacRomanian = 38,
kCFStringEncodingMacCeltic = 39,
kCFStringEncodingMacGaelic = 40,
kCFStringEncodingMacFarsi = 0x8C,
kCFStringEncodingMacUkrainian = 0x98,
kCFStringEncodingMacInuit = 0xEC,
kCFStringEncodingMacVT100 = 0xFC,
kCFStringEncodingMacHFS = 0xFF,
kCFStringEncodingISOLatin1 = 0x0201,
kCFStringEncodingISOLatin2 = 0x0202,
kCFStringEncodingISOLatin3 = 0x0203,
kCFStringEncodingISOLatin4 = 0x0204,
kCFStringEncodingISOLatinCyrillic = 0x0205,
kCFStringEncodingISOLatinArabic = 0x0206,
kCFStringEncodingISOLatinGreek = 0x0207,
kCFStringEncodingISOLatinHebrew = 0x0208,
kCFStringEncodingISOLatin5 = 0x0209,
kCFStringEncodingISOLatin6 = 0x020A,
kCFStringEncodingISOLatinThai = 0x020B,
kCFStringEncodingISOLatin7 = 0x020D,
kCFStringEncodingISOLatin8 = 0x020E,
kCFStringEncodingISOLatin9 = 0x020F,
kCFStringEncodingISOLatin10 = 0x0210,
kCFStringEncodingDOSLatinUS = 0x0400,
kCFStringEncodingDOSGreek = 0x0405,
kCFStringEncodingDOSBalticRim = 0x0406,
kCFStringEncodingDOSLatin1 = 0x0410,
kCFStringEncodingDOSGreek1 = 0x0411,
kCFStringEncodingDOSLatin2 = 0x0412,
kCFStringEncodingDOSCyrillic = 0x0413,
kCFStringEncodingDOSTurkish = 0x0414,
kCFStringEncodingDOSPortuguese = 0x0415,
kCFStringEncodingDOSIcelandic = 0x0416,
kCFStringEncodingDOSHebrew = 0x0417,
kCFStringEncodingDOSCanadianFrench = 0x0418,
kCFStringEncodingDOSArabic = 0x0419,
kCFStringEncodingDOSNordic = 0x041A,
kCFStringEncodingDOSRussian = 0x041B,
kCFStringEncodingDOSGreek2 = 0x041C,
kCFStringEncodingDOSThai = 0x041D,
kCFStringEncodingDOSJapanese = 0x0420,
kCFStringEncodingDOSChineseSimplif = 0x0421,
kCFStringEncodingDOSKorean = 0x0422,
kCFStringEncodingDOSChineseTrad = 0x0423,
kCFStringEncodingWindowsLatin1 = 0x0500,
kCFStringEncodingWindowsLatin2 = 0x0501,
kCFStringEncodingWindowsCyrillic = 0x0502,
kCFStringEncodingWindowsGreek = 0x0503,
kCFStringEncodingWindowsLatin5 = 0x0504,
kCFStringEncodingWindowsHebrew = 0x0505,
kCFStringEncodingWindowsArabic = 0x0506,
kCFStringEncodingWindowsBalticRim = 0x0507,
kCFStringEncodingWindowsVietnamese = 0x0508,
kCFStringEncodingWindowsKoreanJohab = 0x0510,
kCFStringEncodingASCII = 0x0600,
kCFStringEncodingANSEL = 0x0601,
kCFStringEncodingJIS_X0201_76 = 0x0620,
kCFStringEncodingJIS_X0208_83 = 0x0621,
kCFStringEncodingJIS_X0208_90 = 0x0622,
kCFStringEncodingJIS_X0212_90 = 0x0623,
kCFStringEncodingJIS_C6226_78 = 0x0624,
kCFStringEncodingShiftJIS_X0213 = 0x0628,
kCFStringEncodingShiftJIS_X0213_MenKuTen = 0x0629,
kCFStringEncodingGB_2312_80 = 0x0630,
kCFStringEncodingGBK_95 = 0x0631,
kCFStringEncodingGB_18030_2000 = 0x0632,
kCFStringEncodingKSC_5601_87 = 0x0640,
kCFStringEncodingKSC_5601_92_Johab = 0x0641,
kCFStringEncodingCNS_11643_92_P1 = 0x0651,
kCFStringEncodingCNS_11643_92_P2 = 0x0652,
kCFStringEncodingCNS_11643_92_P3 = 0x0653,
kCFStringEncodingISO_2022_JP = 0x0820,
kCFStringEncodingISO_2022_JP_2 = 0x0821,
kCFStringEncodingISO_2022_JP_1 = 0x0822,
kCFStringEncodingISO_2022_JP_3 = 0x0823,
kCFStringEncodingISO_2022_CN = 0x0830,
kCFStringEncodingISO_2022_CN_EXT = 0x0831,
kCFStringEncodingISO_2022_KR = 0x0840,
kCFStringEncodingEUC_JP = 0x0920,
kCFStringEncodingEUC_CN = 0x0930,
kCFStringEncodingEUC_TW = 0x0931,
kCFStringEncodingEUC_KR = 0x0940,
kCFStringEncodingShiftJIS = 0x0A01,
kCFStringEncodingKOI8_R = 0x0A02,
kCFStringEncodingBig5 = 0x0A03,
kCFStringEncodingMacRomanLatin1 = 0x0A04,
kCFStringEncodingHZ_GB_2312 = 0x0A05,
kCFStringEncodingBig5_HKSCS_1999 = 0x0A06,
kCFStringEncodingVISCII = 0x0A07,
kCFStringEncodingKOI8_U = 0x0A08,
kCFStringEncodingBig5_E = 0x0A09,
kCFStringEncodingNextStepLatin = 0x0B01,
kCFStringEncodingNextStepJapanese = 0x0B02,
kCFStringEncodingEBCDIC_US = 0x0C01,
kCFStringEncodingEBCDIC_CP037 = 0x0C02,
kCFStringEncodingUTF7 = 0x04000100,
kCFStringEncodingUTF7_IMAP = 0x0A10,
kCFStringEncodingShiftJIS_X0213_00 = 0x0628
};