Delphi 10：SizeOf（string）问题-Windows vs Android

Question

I want to send TMemoStream from Android to Windows using Indy IdTCPClient and IdTCPServer.

The problem is this:

SizeOf(string) in Android is 4 bytes
SizeOf(string) in Windows 10 is 8 bytes

In android I used this code:

type TMyRecord = record
  x1: string;
  x2: string;
end;

var
  workRecord: TMyRecord;
  rInfo: TMemoryStream;
begin
  workRecord.x1:= 'Hello';
  workRecord.x2:= 'How are you';
  rInfo:= TMemoryStream.Create;

  try
    rInfo.Write(workRecord, SizeOf(workRecord));  //Size of workRecord is 8 bytes
    AndroidTCPClient.IOHandler.Write(workRecord, 0, False);
  finally
    rInfo.Free;
  end;
end;

In Windows 10 I used this code:

type TMyRecord = record
  x1: string;
  x2: string;
end;

type TMyRecord = record
  x1: string;
  x2: string;
end;

var
  workRecord: TMyRecord;
  rInfo: TMemoryStream;
begin
  rInfo:= TMemoryStream.Create;

  try
    AContext.Connection.IOHandler.ReadStream(rInfo, SizeOf(workRecord), False);
    rInfo.Position:= 0;
    rInfo.Read(workRecord, SizeOf(workRecord)); //Size of workRecord is 16 bytes
  finally
    rInfo.Free;
  end;
end;

Anyone advise me how to set up the transmission string from Android to Windows?

Answer 1

sizeof(string) is the size of a pointer. Your Windows program is clearly compiled for 64 bit and so pointers are 8 bytes wide. Your Android program targets 32 bit and pointers are 4 bytes wide.

The bigger problem is that you cannot expect to send pointers from one process to another. The pointers refer to memory in the sending program. They have no meaning in the recipient. You should probably serialize your data, for instance to JSON, and then send that. Then the recipient can deserialize upon receipt.