Question

I’m writing a wrapper for communication with an external binary API. The API uses PDUs (packed binary records) for communication. Strings are arrays of AnsiChar and are zero-terminated:

type 
  TSomePDU = packed record
    //...
    StringField: array[0..XYZ] of AnsiChar;
    //...
  end;
  PSomePDU = ^TSomePDU;

I want to write a FillPDUString procedure that would accept a String and fill the char array, but I want to avoid keeping track of MaxLength wherever the procedure is used, so I need somehow to get the declared array size given a pointer to the field:

function GetMaxSize(const Field: array of AnsiChar): Integer;
begin
  // ???
end;

//...
GetMaxSize(ARecord.StringField);

Is this possible?

Answer 1

If I understand you correctly, then you can use Delphi’s Length function

Here’s how to get the length:

function GetMaxSize(const Value: PSomePDU): Integer; 
begin
  Result := Length(Value.StringField);
end;