System.SysUtils.TStringHelper 详解，注意事项

大小写转换:

---

function ToLower: string;
function ToLower(LocaleID: TLocaleID): string;
function ToLowerInvariant: string;
function ToUpper: string;
function ToUpper(LocaleID: TLocaleID): string;
function ToUpperInvariant: string;

class function LowerCase(const S: string): string;
class function LowerCase(const S: string; LocaleOptions: TLocaleOptions): string;
class function UpperCase(const S: string): string;
class function UpperCase(const S: string; LocaleOptions: TLocaleOptions): string;
//--------------------------------------------------------------------------------
var
  str: string;
begin
  str := 'Delphi';
  str := str.ToLower; // delphi
  str := str.ToUpper; // DELPHI
end;

---

清除两边空格或指定字符:

---

function Trim: string;
function TrimLeft: string;
function TrimRight: string;
function Trim(const TrimChars: array of Char): string;
function TrimLeft(const TrimChars: array of Char): string;
function TrimRight(const TrimChars: array of Char): string;
//--------------------------------------------------------------------------------
var
  str1, str2: string;
begin
  str1 := '   Delphi 10000   ';

  str2 := str1.TrimLeft;  // 'Delphi 10000   '
  str2 := str1.TrimRight; // '   Delphi 10000'
  str2 := str1.Trim;      // 'Delphi 10000'

  str2 := str1.Trim([' ', '0']); // 'Delphi 1'
end;

---

字符串对比:

---

function CompareTo(const strB: string): Integer;

class function Compare(const StrA: string; const StrB: string): Integer;
class function CompareText(const StrA: string; const StrB: string): Integer;
class function Compare(const StrA: string; const StrB: string; LocaleID: TLocaleID): Integer;
class function Compare(const StrA: string; const StrB: string; IgnoreCase: Boolean): Integer;
class function Compare(const StrA: string; const StrB: string; IgnoreCase: Boolean; LocaleID: TLocaleID): Integer;
class function Compare(const StrA: string; IndexA: Integer; const StrB: string; IndexB: Integer; Length: Integer): Integer;
class function Compare(const StrA: string; IndexA: Integer; const StrB: string; IndexB: Integer; Length: Integer; LocaleID: TLocaleID): Integer;
class function Compare(const StrA: string; IndexA: Integer; const StrB: string; IndexB: Integer; Length: Integer; IgnoreCase: Boolean): Integer;
class function Compare(const StrA: string; IndexA: Integer; const StrB: string; IndexB: Integer; Length: Integer; IgnoreCase: Boolean; LocaleID: TLocaleID): Integer;
class function CompareOrdinal(const StrA: string; const StrB: string): Integer;
class function CompareOrdinal(const StrA: string; IndexA: Integer; const StrB: string; IndexB: Integer; Length: Integer): Integer;
//--------------------------------------------------------------------------------
var
  str1, str2: string;
  n: Integer;
begin
  str1 := 'ABC 123';
  str2 := 'abc 123';

  n := str1.CompareTo(str2);              // -32

  n := str1.Compare(str1, str2);          // 1
  n := str1.CompareText(str1, str2);      // 0; 相同

  n := str1.Compare(str1, str2, True);    // 0; 不区分大小写
  n := str1.CompareOrdinal(str1, str2);   // -32

  n := str1.Compare(str1, 4, str2, 4, 3); // 0; 只对比后三位
end;

---

搜索字符串:

---

function IndexOf(value: Char): Integer;
function IndexOf(const Value: string): Integer;
function IndexOf(Value: Char; StartIndex: Integer): Integer;
function IndexOf(const Value: string; StartIndex: Integer): Integer;
function IndexOf(Value: Char; StartIndex: Integer; Count: Integer): Integer;
function IndexOf(const Value: string; StartIndex: Integer; Count: Integer): Integer;
function IndexOfAny(const AnyOf: array of Char): Integer;
function IndexOfAny(const AnyOf: array of Char; StartIndex: Integer): Integer;
function IndexOfAny(const AnyOf: array of Char; StartIndex: Integer; Count: Integer): Integer;

function LastIndexOf(Value: Char): Integer;
function LastIndexOf(const Value: string): Integer;
function LastIndexOf(Value: Char; StartIndex: Integer): Integer;
function LastIndexOf(const Value: string; StartIndex: Integer): Integer;
function LastIndexOf(Value: Char; StartIndex: Integer; Count: Integer): Integer;
function LastIndexOf(const Value: string; StartIndex: Integer; Count: Integer): Integer;
function LastIndexOfAny(const AnyOf: array of Char): Integer;
function LastIndexOfAny(const AnyOf: array of Char; StartIndex: Integer): Integer;
function LastIndexOfAny(const AnyOf: array of Char; StartIndex: Integer; Count: Integer): Integer;
//--------------------------------------------------------------------------------
var
  str: string;
  n: Integer;
begin
  str := 'A1 A2 A3 A4';

  n := str.IndexOf('A');     // 0
  n := str.LastIndexOf('A'); // 9
  n := str.IndexOf('B');     // -1; 没找到

  n := str.IndexOf('A', 1, str.Length - 1);                  // 3
  n := str.LastIndexOf('A', str.Length - 1, str.Length - 1); // 9

  n := str.IndexOfAny(['1', '2', '3', '4']);     // 1
  n := str.LastIndexOfAny(['1', '2', '3', '4']); // 10
end;

---

是否包含:

---

function Contains(const Value: string): Boolean;

function StartsWith(const Value: string): Boolean;
function StartsWith(const Value: string; IgnoreCase: Boolean): Boolean;

function EndsWith(const Value: string): Boolean;
function EndsWith(const Value: string; IgnoreCase: Boolean): Boolean;

class function EndsText(const ASubText, AText: string): Boolean;
//--------------------------------------------------------------------------------
var
  str: string;
  b: Boolean;
begin
  str := 'Delphi XE4';

  b := str.Contains('XE'); // True
  b := str.Contains('xe'); // False

  b := str.StartsWith('delphi');       // False
  b := str.StartsWith('delphi', True); // True

  b := str.EndsWith('XE4');            // True

  b := str.EndsText('xe4', str);       // True
end;

---

添加或解除引号:

---

function QuotedString: string;
function QuotedString(const QuoteChar: Char): string;

function DeQuotedString: string;
function DeQuotedString(const QuoteChar: Char): string;
//--------------------------------------------------------------------------------
var
  str1, str2: string;
begin
  str1 := 'Delphi';

  str2 := str1.QuotedString;        // 'Delphi'
  str2 := str1.QuotedString('"');   // "Delphi"

  str1 := '"Delphi"';
  str2 := str1.DeQuotedString('"'); // Delphi
end;

---

适宽处理:

---

function PadLeft(TotalWidth: Integer): string;
function PadLeft(TotalWidth: Integer; PaddingChar: Char): string;
function PadRight(TotalWidth: Integer): string;
function PadRight(TotalWidth: Integer; PaddingChar: Char): string;
//--------------------------------------------------------------------------------
var
  str: string;
begin
  str := '1';
  str := str.PadLeft(4, '0'); // 0001
end;

---

插入（startIndex从0开始，严重注意，insert是直接把原来的字符串销毁，生成一个新的字符串）：

function Insert(StartIndex: Integer; const Value: string): string;

procedure TForm3.btn2Click(Sender: TObject);
var
  s1, s2: string;
begin
  s1 := '123456789';

  s2 := s1.Insert(0, '0'); //startIndex从0开始

  mmo1.Lines.Add(s1); // 0123456789，插入是直接把原来的字符串销毁掉，直接生成新的字符串

  mmo1.Lines.Add(s2); //0123456789,

end;

删除（startIndex是从0开始，严重注意，remove是生成【另】一个新的字符串，原来的字符串不变）:

function Remove(StartIndex: Integer): string;
function Remove(StartIndex: Integer; Count: Integer): string;

procedure TForm3.btn1Click(Sender: TObject);
var
  s1, s2: string;
begin
  s1 := '123456789';

  s2 := s1.Remove(1, 1); //Remove 会形成新的字符串，原来的s1不变

  mmo1.Lines.Add(s1.Remove(0, 1)); // 23456789，Remove是下标从0开始

  mmo1.Lines.Add(s1.Remove(1, 1));

  mmo1.Lines.Add(s1); //'123456789'，可见s1并没有发生改变

  mmo1.Lines.Add(s2);

end;

---

截取（startIndex是从0开始）:

---

function Substring(StartIndex: Integer): string;
function Substring(StartIndex: Integer; Length: Integer): string;

procedure TForm3.btn1Click(Sender: TObject);
var
  s: string;
begin
  s := '123456';
  mmo1.Lines.Add(s[1]); //1，下标从1开始
  mmo1.Lines.Add(s.Substring(1, 1)); //2，下标从0开始

end;

subString的下标是从0开始的严重留意。。。

替换:

---

function Replace(OldChar: Char; NewChar: Char): string;
function Replace(OldChar: Char; NewChar: Char; ReplaceFlags: TReplaceFlags): string;
function Replace(const OldValue: string; const NewValue: string): string;
function Replace(const OldValue: string; const NewValue: string; ReplaceFlags: TReplaceFlags): string;
//--------------------------------------------------------------------------------
var
  str1, str2: string;
begin
  str1 := 'ABC ABC ABC';
  str2 := str1.Replace('A', '*');                 // *BC *BC *BC
  str2 := str1.Replace('A', '*', [rfIgnoreCase]); // *BC ABC ABC
end;

---

分割:

---

function Split(const Separator: array of Char): TArray<string>;
function Split(const Separator: array of Char; Count: Integer): TArray<string>;
function Split(const Separator: array of Char; Options: TStringSplitOptions): TArray<string>;
function Split(const Separator: array of string; Options: TStringSplitOptions): TArray<string>;
function Split(const Separator: array of Char; Count: Integer; Options: TStringSplitOptions): TArray<string>;
function Split(const Separator: array of string; Count: Integer; Options: TStringSplitOptions): TArray<string>;
//--------------------------------------------------------------------------------
var
  str: string;
  arr: TArray<string>;
begin
  str := 'A-1,B-2,,,C-3,D-4';

  arr := str.Split([',']);                                   // arr[0] = A-1; Length(arr) = 6
  arr := str.Split([','], TStringSplitOptions.ExcludeEmpty); // 忽略空项; Length(arr) = 4
  arr := str.Split([','], 2);                                // 只提取前 2

  arr := str.Split([',', '-'], ExcludeEmpty); //arr[0] = A; Length(arr) = 8

  arr := str.Split([',,,'], None);            // 分隔符可以是一个字符串数组
end;

---

连接:

---

class function Join(const Separator: string; const values: array of const): string;
class function Join(const Separator: string; const Values: array of string): string;
class function Join(const Separator: string; const Values: IEnumerator<string>): string;
class function Join(const Separator: string; const Values: IEnumerable<string>): string;
class function Join(const Separator: string; const value: array of string; StartIndex: Integer; Count: Integer): string;
//--------------------------------------------------------------------------------
var
  S: string;
  str: string;
  strArr: TArray<string>;
begin
  str := 'A1,B2,C3,,,,D4,E5,F6,G7';
  strArr := str.Split([','], ExcludeEmpty);

  str := S.Join('-', strArr);             // A1-B2-C3-D4-E5-F6-G7

  str := S.Join('; ', [1,2,3,4,5]);       // 1; 2; 3; 4; 5

  str := S.Join(',', ['abc', 123, true]); // abc,123,True
end;

---

类型转换:

---

function ToBoolean: Boolean;
function ToInteger: Integer;
function ToSingle: Single;
function ToDouble: Double;
function ToExtended: Extended;

class function ToBoolean(const S: string): Boolean;
class function ToInteger(const S: string): Integer;
class function ToSingle(const S: string): Single;
class function ToDouble(const S: string): Double;
class function ToExtended(const S: string): Extended;

class function Parse(const Value: Integer): string;
class function Parse(const Value: Int64): string;
class function Parse(const Value: Boolean): string;
class function Parse(const Value: Extended): string;
//--------------------------------------------------------------------------------
var
  S: string;
  str: string;
  n: Integer;
  b: Boolean;
  f: Double;
begin
  str := S.Parse(123);
  n := str.ToInteger;  // 123
  b := str.ToBoolean;  // True

  str := S.Parse(True);
  b := str.ToBoolean;  // True
  n := str.ToInteger;  // -1

  str := S.Parse(3.14159260000);
  f := str.ToDouble;  //3.1415926
end;

---

定界符:

---

function IsDelimiter(const Delimiters: string; Index: Integer): Boolean;
function LastDelimiter(const Delims: string): Integer;
//--------------------------------------------------------------------------------
var
  str: string;
  b: Boolean;
  n: Integer;
begin
  str := 'http://del.cnblogs.com';

  b := str.IsDelimiter(':', 4);  // True
  b := str.IsDelimiter('//', 5); // True

  n := str.LastDelimiter('.');   // 18
  n := str.IndexOf('.');         // 10
end;

---

空字符串:

---

const Empty = '';

function IsEmpty: Boolean;

class function IsNullOrEmpty(const Value: string): Boolean;
class function IsNullOrWhiteSpace(const Value: string): Boolean;
//--------------------------------------------------------------------------------
var
  S: string;
  str: string;
  b: Boolean;
begin
  str := '       ';

  b := str.IsEmpty;               // False
  b := S.IsNullOrWhiteSpace(str); // True
end;

---

String 与 Char:

---

class function Create(C: Char; Count: Integer): string;
class function Create(const Value: array of Char; StartIndex: Integer; Length: Integer): string;
class function Create(const Value: array of Char): string;

property Chars[Index: Integer]: Char read GetChars;
property Length: Integer read GetLength;

function CountChar(const C: Char): Integer;

function ToCharArray: TArray<Char>;
function ToCharArray(StartIndex: Integer; Length: Integer): TArray<Char>;

procedure CopyTo(SourceIndex: Integer; var destination: array of Char; DestinationIndex: Integer; Count: Integer);
//--------------------------------------------------------------------------------
var
  S: string;
  str, str2: string;
  charArr: TCharArray;
  n: Integer;
  c: Char;
begin
  str := 'ABC';
  n := str.Length;   // 3
  c := str.Chars[0]; // A = str[1]

  str := S.Create('A', 7); // AAAAAAA

  charArr := 'ABCDEFG'.ToCharArray;
  str := s.Create(charArr);       // ABCDEFG
  str := S.Create(charArr, 1, 3); // BCD

  charArr := '1234567890'.ToCharArray;
  str := 'ABCDEFG';
  str.CopyTo(1, charArr, 2, 3);
  str := S.Create(charArr);       // 12BCD67890
end;

---

其他:

---

function Equals(const Value: string): Boolean;
function GetHashCode: Integer;

class function Equals(const a: string; const b: string): Boolean;
class function Format(const Format: string; const args: array of const): string;
class function Copy(const Str: string): string;