Delphi7中Unicode,ANSI,UTF编码问题

注解：
　　ANSI     'American Standard Code for Information Interchange' 美国信息互换标准代码 ANSI的'Ascii'编码
　　Unicode 'Universal Multiple-Octet Coded Character Set' 简称 UCS, 俗称 'Unicode'
　　UTF       'UCS Transfer Format'
　　DBCS    'Double Byte Charecter Set' 双字节字符集

相关重要函数过程:
WinAPI:
　　MultiByteToWideChar WideCharToMultiByte
　　相关参数(CodePage)

　　　　CP_ACP ANSI code page
　　　　CP_MACCP Not supported
　　　　CP_OEMCP OEM code page
　　　　CP_SYMBOL Not supported
　　　　CP_THREAD_ACP Not supported
　　　　CP_UTF7 UTF-7 code page
　　　　CP_UTF8 UTF-8 code page

单元System.pas:
function StringToWideChar(const Source: string; Dest: PWideChar; DestSize: Integer): PWideChar;
function WideCharToString(Source: PWideChar): string;
function WideCharLenToString(Source: PWideChar; SourceLen: Integer): string;
procedure WideCharToStrVar(Source: PWideChar; var Dest: string);
procedure WideCharLenToStrVar(Source: PWideChar; SourceLen: Integer; var Dest: string);

type
　　UCS2Char = WideChar; PUCS2Char = PWideChar;
　　UCS4Char = type LongWord;
　　UCS4String = array of UCS4Char;
function PUCS4Chars(const S: UCS4String): PUCS4Char;
function WideStringToUCS4String(const S: WideString): UCS4String;
function UCS4StringToWideString(const S: UCS4String): WideString;

function UnicodeToUtf8(Dest: PChar; Source: PWideChar; MaxBytes: Integer): Integer; overload; deprecated;
function Utf8ToUnicode(Dest: PWideChar; Source: PChar; MaxChars: Integer): Integer; overload; deprecated;

function UnicodeToUtf8(Dest: PChar; MaxDestBytes: Cardinal; Source: PWideChar; SourceChars: Cardinal): Cardinal; overload;
function Utf8ToUnicode(Dest: PWideChar; MaxDestChars: Cardinal; Source: PChar; SourceBytes: Cardinal): Cardinal; overload;
function UTF8Encode(const WS: WideString): UTF8String;
function UTF8Decode(const S: UTF8String): WideString;

function AnsiToUtf8(const S: string): UTF8String;
function Utf8ToAnsi(const S: UTF8String): string;

原文出处：https://www.cnblogs.com/kmhr/p/8443967.html