Author: Jonas Bilinkevicius

How to create a random string

Answer:

Solve 1:

1   var
2     LoopInt: Integer;
3     DirName, FullName, RanStr: string;
4     FileSavedTo: TextFile;
5     { Length of string to create }
6     RandArray: array[0..4087] of Char;
7     FirstCount: Extended;
8   begin
9     FirstCount := GetTickCount;
10    Label2.Caption := '';
11    Randomize;
12    RanStr := '';
13    DirName := Directory95ListBox1.Directory;
14    if DirName[Length(DirName)] <> '\' then
15      DirName := DirName + '\';
16    FullName := DirName + Edit1.Text;
17    if FileExists(FullName) then
18      DeleteFile(FullName);
19    for LoopInt := Low(RandArray) to High(RandArray) do
20    begin
21      RanStr := RanStr + Chr(Random(255 - 32 + 1) + 32);
22    end;
23    AssignFile(FileSavedTo, FullName);
24    if FileExists(FullName) then
25      Reset(FileSavedTo)
26    else
27      Rewrite(FileSavedTo);
28    Writeln(FileSavedTo, RanStr);
29    CloseFile(FileSavedTo);
30    Label2.Caption := ' Done ';
31    Label4.Caption := FloatToStr((GetTickCount - FirstCount) / 1000);
32    FileListBox1.Update;
33  end;


Randomize should be called only once in an application. You should therefore put 
the above code into the form's OnCreate event for example, or remove Randomize from 
the above code and call it from the form's OnCreate event handler.


Solve 2:

This routine creates passwords from a string table with selected chars. Note: The 
password length must be shorter than the given string table length.
34  
35  {Call Randomize only once at application start.}
36  
37  procedure TForm1.FormCreate(Sender: TObject);
38  begin
39    Randomize;
40  end;
41  
42  function RandomPwd(PWLen: integer): string;
43  {Set the table of chars to be used in passwords}
44  const
45    StrTable: string = '!#$%&/()=?@<>|{[]}\*~+#;:.-_' + 'ABCDEFGHIJKLMabcdefghijklm' +
46    '0123456789' + 'ÄÖÜäöüß' + 'NOPQRSTUVWXYZnopqrstuvwxyz';
47  var
48    N, K, X, Y: integer;
49  begin
50    {Check the maximum password length}
51    if (PWlen > Length(StrTable)) then
52      K := Length(StrTable) - 1
53    else
54      K := PWLen;
55    SetLength(result, K); {Set the length of the result string}
56    Y := Length(StrTable); {Table length for inner loop}
57    N := 0; {Loop start value}
58    while N < K do
59    begin {Loop to create K chars}
60      X := Random(Y) + 1; {Get next random char}
61      {Check for the presence of this char in the result string}
62      if (pos(StrTable[X], result) = 0) then
63      begin
64        inc(N); {Not found }
65        Result[N] := StrTable[X];
66      end;
67    end;
68  end;
69  
70  //Used like this:
71  
72  procedure TForm1.Button1Click(Sender: TObject);
73  var
74    cPwd: string;
75  begin
76    {e.g. create a random password string with 30 chars}
77    cPwd := RandomPwd(30);
78    { ... }
79  end;