Remove invalid url characters with TRegExpr - regex

Question

Good day. I can't seem to find an example of how use the TRegExpr component to do a simple replace of invalid characters. For example i have a string = 'abcdeg3fghijk'; and i want to replace all the characters that are invalid such as the numerial '3', how would process this with TRegExpr to replace all invalid characters. My intention is learn how to use the TRegExpr to build a simple url cleaner/validator.
procedure TForm1.Button3Click(Sender: TObject);
var
RegExp: TRegExpr;
astr:string;
begin
astr:='h"ttp://ww"w.msn."com~~~';
// I want to clean the string to remove all non valid chars
//this is where I am lost
RegExp:=TRegExpr.Create;
try
RegExp.Expression:=RegExpression;
finally
RegExp.Free;
end;
end;

Answer 1

Judging from the commments and the question edit, you are trying to work out how to perform a replacement using a regex. The function you need is TRegEx.Replace.
There are lots of overloads. The simplest to use are the class functions. For example:
NewValue := TRegEx.Replace(OldValue, '3', '4');
will replace all occurrences of 3 with 4.
Or if you want to use the instance method approach, do it like this:
var
RegEx: TRegEx;
....
RegEx.Create('3');
NewValue := RegEx.Replace(OldValue, '4');
Remember that TRegEx is a record, a value type. There's no Free to call and no need for try/finally. I personally regard Create as very badly named. I would have preferred Initialize if I had been designing the TRegEx type.
Using the instance method approach allows the expression to be compiled and that speeds up performance for repeated matching of the same expression to different input data. I don't know whether that would matter for you. If not then use the class function interface which is simpler to use.
You'll obviously extend this to use a useful regex for your replacement!
The documentation for the PCRE regex flavour that Delphi uses is here: http://www.regular-expressions.info/pcre.html