...
type
 TIntegerFile = file of Integer; // 允许你将整数写入文件
 TPCharFile = file of PChar; // PChars写入到文件
 TStringFile = file of String; // 字符串写入到文件
...

{$I-} // 关闭检查。将所有的错误存入IOResult变量
{$I+} // 把它重新打开，将导致EInOutError异常

program FileTest;

{$mode objfpc} // 不要忘了这个

uses
 Sysutils;

var
 FileVar: TextFile;

begin
  WriteLn('File Test');
  AssignFile(FileVar, 'Test.txt'); // 你不需要输出 .txt 但现在需要
  {$I+} // 使用异常处理
  try  
    Rewrite(FileVar);  // 创建文件
    Writeln(FileVar,'Hello');
    // Use CloseFile rather than Close as Close is used in other units as well
    CloseFile(FileVar);
  except
    on E: EInOutError do
    begin
     Writeln('File handling error occurred. Details: '+E.ClassName+'/'+E.Message);
    end;    
  end;
  WriteLn('Program finished. Press enter to stop.');  
  ReadLn;
end.

program EditFile;

{$mode objfpc}

uses
 Sysutils;

var
 File1: TextFile;
 
begin
  WriteLn('Append file');
  {$I+}
  try
    AssignFile(File1, 'File.txt');
    { 
    我这里测试时，原版示例不能执行报错 Error: Wrong number of parameters specified for call to "Append"
    在Lazarus 1.2.2，FPC2.6.4上
    }
    // Append(File1, 'adding some text...'); 
    { 修改后的程序 }
    Append(File1);
    Writeln(FileVar,'adding some text...'); 
    Writeln
    CloseFile(File1);
  except
    on E: EInOutError do
    begin
     Writeln('File handling error occurred. Details: '+E.ClassName+'/'+E.Message);
    end;    
  end;
  WriteLn('Program finished. Press enter to stop.');  
  Readln;
end.

program ReadFile;

{$mode objfpc}

uses
 Sysutils;

var
 File1: TextFile;
 Str: String;

begin
  Writeln('File Reading:');
  AssignFile(File1, 'File.txt');
  {$I+}
  try
    Reset(File1);
    repeat
      Readln(File1, Str); // 从文件中读取一行
      Writeln(Str); // 显示这行
    until(EOF(File1)); // EOF(文件结束)程序将继续读取直到文件结尾。
    CloseFile(File1);
  except
    on E: EInOutError do
    begin
     Writeln('File handling error occurred. Details: '+E.ClassName+'/'+E.Message);
    end;    
  end;
  WriteLn('Program finished. Press enter to stop.');  
  Readln;
end.

var
  Buffer: array[0..9999] of Byte;
begin
  with TFileStream.Create('SomeFile.bin', fmCreate) do 
  try
    Seek('Hello');
    Write(Buffer, SizeOf(Buffer));
  finally
    Free;
  end;
end;

begin
  with TMemoryStream.Create do 
  try
    LoadFromFile('SomeFile.bin');
    Seek(0, soEnd);
    Write(Ord('A'), 1);
    SaveToFile('SomeFile.bin');
  finally
    Free;
  end;
end;

var
  TotalBytesRead, BytesRead : Int64;
  Buffer : array [0..4095] of byte;  // 或 array [0..4095] 为 char
  FileStream : TFileStream;

try
  FileStream := TFileStream.Create;
  FileStream.Position := 0;  // 确保在文件开始位置
  while TotalBytesRead <= FileStream.Size do  // 当总读取大小 <= 文件大小
  begin
    BytesRead := FileStream.Read(Buffer,sizeof(Buffer));  // 读取 4096 字节数据
    inc(TotalBytesRead, BytesRead);                       // 增加 TotalByteRead 缓冲区的大小，也就是说 4096 字节
    // 做一些与缓冲数据相关的操作
  end;

function FileCopy(Source, Target: string): boolean;
// 复制文件 source 到 target；覆盖目标文件
// 在内存中缓存整个文件
// 成功返回 true，失败返回false
var
  MemBuffer: TMemoryStream;
begin
  result:=false;
  MemBuffer:=TMemoryStream.Create;
  try
    try
      MemBuffer.LoadFromFile(Source);
      MemBuffer.Position:=0;
      MemBuffer.SaveToFile(Target); //可能是源文件相同
      result:=true;
    except
      result:=false; //忽略异常，转换为错误代码
    end;
  finally
    MemBuffer.Free;
  end;
end;

begin
  with TStringList.Create do 
  try
    Add('Hello');
    SaveToFile('SomeFile.txt');
  finally
    Free;
  end;
end;

procedure SaveStringToPath(theString, filePath: String);
var
  textFile: TFileStream = nil;
  textLength: integer;
  stringBuffer: ^String;
begin
  textLength := length(theString);
  try
    textFile := TFileStream.Create(filePath, fmOpenWrite or fmCreate);
    { write string to stream while avoiding to write the initial length }
    { 写字符串到流，同时避免写入超过最初长度 }
    stringBuffer := @theString + 1;
    textFile.WriteBuffer(stringBuffer^, textLength);
  finally
    if textFile <> nil then textFile.Free;
  end;
end;