VALIDATING INPUT USING 'CHARACTER SET' VARIABLES...
Richard Nov '98
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'FileName' example.
bearing in mind that the following characters are not allowed in filenames
\ / : * ? " < > | (along with lots of unprintably BAD characters -if you didn't
laugh you're an anorak) then we can assume that the valid filename set includes
characters from the '!' (ascii 33) to the '~' (ascii 126) MINUS the above
baddies. So using sets we can set things up like this:
type
TpossFNameChars = set of Char;
var
validFNameChars: TpossFNameChars;
badFNameChars: TpossFNameChars;
begin
badFNameChars := ['\','/',':','*','?','"','<','>','|'];
validFNameChars := ['!'..'~'];
validFNameChars := validFNameChars - badFNameChars;
and then we might say something like this:
if not(charArray[index] in validFNameChars) then
begin
{whatever}
end;
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Example of a whole procedure using a similar technique
function ValidInput(InputText : TCaption) : Boolean;
{the built-in Delphi IsAlpha() function does not trap things like}
{quotation marks... -this is home-made and better}
type
TvalidInputChars = set of Char;
var
i,len : Integer;
validInputChars: TvalidInputChars;
begin
{define the SET of valid input characters}
validInputChars := ['A'..'Z', 'a'..'z'];
i := 1;
{Note: Delphi puts text from an input box into the box's .Text property when}
{focus shifts away from that box, and the TYPE of this text property is}
{TCaption}
len := Length(InputText);
{the first byte of yer actual string here contains length information...}
{so go from index 1 upwards...}
for i := 1 to len do
begin
if InputText[i] in validInputChars then
begin
Result := True
end
else
begin
Result := False;
Break;
end;
end;
end;
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and another example:
function TForm1.ValidateInput(inputString: String): Boolean;
{ensure that each character of the user's input is a character with the
following characteristics: it must be a character form the 'normal' ASCII
range of 0 to 127, it must be a VISIBLE character, and it must also be in
the ranges 'A' to 'Z' and 'a' to 'z'!!!...}
type
TplainASCIIChars = set of Char;
var
plainASCIIChars: TplainASCIIChars;
inputLen: Integer;
badChars: Boolean;
begin
plainASCIIChars := [Chr(65)..Chr(90), Chr(97)..Chr(122)];
badChars := False;
inputLen := Length(inputString);
{copy the search pattern into an array before validating it...}
for i := 1 to inputLen do
begin
tempArray[i - 1] := searchPatt[i];
end;
tempArray[i - 1] := #0;
{and look for dodgy characters in the search string...}
for i := 0 to (inputLen - 1) do
begin
if not(tempArray[i] in plainASCIIChars) then badChars := True;
end;
if (badChars = True) then Result := False
else Result := True;
end.