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

Solution

There are a couple of problems with your code:

1. You are type-casting your input AnsiString incorrectly to PWideChar, so you are calling the wrong overload of HexToBin(). PWideChar should be PAnsiChar instead.

2. 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;

Comments

[Sertac Akyuz]

Point '3' is an error in documentation. HexToBin accounts for uppercase letters since at least D7 (older version I can check is D3, which doesn't have the function at all).

[Remy Lebeau]

@SertacAkyuz: you are right, I misread the code when I checked it before posting. FYI, the support of uppercase goes all the way back to at least Delphi 5, if not 4 (but it didn't ignore non-hex characters #58..#64,#91..#96 until Delphi 2009).

[Remy Lebeau]

@SertacAkyuz: I reported the documentation error: RSP-19625

[peiman F.]

firemonkey in android dont have PAnsiChar and AnsiString

[Remy Lebeau]

@peimanF. So just use String and PChar instead. You don't need AnsiString support to use hex strings. Bin2Hex() and Hex2Bin() are overloaded for Unicode strings. Otherwise, install Andreas Hausladen's ByteStrings patch.