System.Copy 从字符串或数组中复制

function Copy(
  S: String;      {字符串或动态数组}
  Index: Integer; {起始位置}
  Count: Integer  {Copy 个数}
): String;        {如果参数 S 是动态数组, 这里也应该返回动态数组}

举例:

---

//从字符串中提取
var
  ss,s: string;
begin
  ss := 'CodeGear Delphi 2007';
  s := Copy(ss,5,4);
  ShowMessage(s);   {Gear}
end;


//从静态字符数组中截取字符串
var
  arr: array[0..25] of Char;
  s: string;
  i: Integer;
begin
  {给 arr 装入 26 个大写字母}
  for i := Low(arr) to High(arr) do
    arr[i] := Chr(i+65);
    
  {提取}
  s := Copy(arr, 1, 3);
  ShowMessage(s);       {ABC}
end;


//从动态数组到动态数组
var 
  arr1,arr2 : array of Integer;
  i: Integer;
begin
  {设定数组大小}
  SetLength(arr1, 10);

  {给数组赋值}
  for i := Low(arr1) to High(arr1) do
    arr1[i] := i;

  {执行 Copy; 注意: 之前没有给 arr2 设置大小, 就是设置了, 在这里也会被重置!}
  arr2 := Copy(arr1, 0, 3);

  for i in arr2 do
    ShowMessage(IntToStr(i)); {会分别显示: 0、1、2}
end;


//关于起始位置(仅对字符串, 动态数组另当别论)
const
  ss = 'ABCDEFG';
var
  s: string;
begin
  s := Copy(ss, 1, 3);
  ShowMessage(s);        {ABC}
  s := Copy(ss, 0, 3);
  ShowMessage(s);        {ABC}
  s := Copy(ss, -1, 3);
  ShowMessage(s);        {ABC}
  s := Copy(ss, -100, 3);
  ShowMessage(s);        {ABC}
end;


//关于 Copy 个数
const
  ss = 'ABCDEFG';
var
  s: string;
begin
  s := Copy(ss, 2, 6);
  ShowMessage(s);               {BCDEFG}
  s := Copy(ss, 2, Length(ss));
  ShowMessage(s);               {BCDEFG}
  s := Copy(ss, 2, MaxInt);
  ShowMessage(s);               {BCDEFG}
end;

System 单元下的公用函数目录

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