Delphi Tokyo - Function: String to Hex and Hex to String - string

Question

The function below works perfectly to convert string to hexadecimal:
function String2Hex(const Buffer: AnsiString): string;
begin
SetLength(Result, Length(Buffer) * 2);
BinToHex(#Buffer[1], PWideChar(#Result[1]), Length(Buffer));
end;
ShowMessage(String2Hex('stackoverflow'));
This result: "737461636B6F766572666C6F77"
The problem is in the function of converting hexadecimal to string:
function Hex2String(const Buffer: AnsiString): string;
begin
SetLength(Result, Length(Buffer) div 2);
HexToBin(PWideChar(#Buffer[1]), #Result[1], Length(Buffer));
end;
ShowMessage(Hex2String('737461636B6F766572666C6F77'));
The result should be "stackoverflow" but nothing happens.
Could someone help me?

Answer 1

There are a couple of problems with your code:
You are type-casting your input AnsiString incorrectly to PWideChar, so you are calling the wrong overload of HexToBin(). PWideChar should be PAnsiChar instead.
The BufSize parameter of HexToBin() specifies the number of bytes the output buffer expects to receive, but you are passing it the number of characters in the hex string instead.
Also, since String2Hex() takes an AnsiString and returns a UnicodeString, Hex2String() should take UnicodeString and return an AnsiString to match.
Try this instead:
function String2Hex(const Buffer: AnsiString): string;
begin
SetLength(Result, Length(Buffer) * 2);
BinToHex(PAnsiChar(Buffer), PChar(Result), Length(Buffer));
end;
function Hex2String(const Buffer: string): AnsiString;
begin
SetLength(Result, Length(Buffer) div 2);
HexToBin(PChar(Buffer), PAnsiChar(Result), Length(Result));
end;
var
hex: string;
str: AnsiString;
begin
hex := String2Hex('stackoverflow');
ShowMessage(hex); // shows '737461636B6F766572666C6F77'
str := Hex2String(hex);
ShowMessage(str); // shows 'stackoverflow'
end;