function Tform1.Test;
var
fs:TFileStream;
fs2:TFileStream;
fs3:TFileStream;
str:string;
ms:TMemoryStream;
ms2:TMemoryStream;
sr:TStream;
begin
    //TFileStream创建文本文件
    str:='文件操作';
    fs:=TFileStream.Create('c:\1.txt',fmCreate);
    fs.WriteBuffer((PChar(str))^,Length(str));
    fs.Free;
    
    //TFileStream读取文本文件
    fs:=TFileStream.Create('c:\1.txt',fmOpenRead);
    SetLength(str,fs.size);
    fs.ReadBuffer((PChar(str))^,fs.Size);
    ShowMessage(str);
    fs.Free;

    //TFileStream读取文本文件
    ms:=TMemoryStream.Create;
    ms.LoadFromFile('c:\1.txt');
    SetLength(str,ms.size);
    ms.ReadBuffer((PChar(str))^,ms.size);
    ms.Free;
    ShowMessage(str);

    //TMemoryStream创建文本文件
    str:='文件操作';
    ms:=TMemoryStream.Create;
    ms.WriteBuffer((PChar(str))^,Length(str));
    ms.SaveToFile('c:\2.txt');
    ms.Free;

    //TMemoryStream文件合并
    ms:=TMemoryStream.Create;
    ms.LoadFromFile('c:\1.txt');
    ms.Position:=ms.Size;//移动文件指针
    ms2:=TMemoryStream.Create;
    ms2.LoadFromFile('c:\2.txt');
    ms.CopyFrom(ms2,0);
    ms.SaveToFile('c:\3.txt');
    ms.Free;
    ms2.Free;
end;

TFileStream和TMemoryStream分别读取、创建、合并文件