Delphi：向文件写入/读取变量和记录

Question

在 XE8 中处理我的项目时，我需要保存和读取自定义项目文件，这些文件存储不同类型的变量和记录。最初，我解决这个问题的方法似乎有效，但在实际项目中却被证明是错误的。

我创建文件、存储“类别”记录的方法：

var 
SavingStream: TFileStream;
         i,j: Integer;
begin
SavingStream:=TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
SavingStream.Position:=0;
i:=Length(Categories);                 **// storing size of an array in a temp variable**
SavingStream.WriteBuffer(i,SizeOf(i)); **// for some reason i couldn't save it directly**
for i:=0 to Length(Categories)-1 do
   begin         
   **{ String }**
   SavingStream.WriteBuffer(Categories[i].Name,SizeOf(Categories[i].Name));  
   **{ Integer }**   
   SavingStream.WriteBuffer(Categories[i].ID,SizeOf(Categories[i].ID));
   **{ Boolean }**
   SavingStream.WriteBuffer(Categories[i].Default,SizeOf(Categories[i].Default))
   **{ Same routine for dynamic array }**
   j:=Length(Categories[i].ChildrenType);
   SavingStream.WriteBuffer(j,SizeOf(j));
   if j>=1 then for j:=0 to Length(Categories[i].ChildrenType)-1 do SavingStream.WriteBuffer(Categories[i].ChildrenType[j],SizeOf(Categories[i].ChildrenType[j]));
   end;
end;

然后阅读它：

var 
SavingStream: TFileStream;
         i,j: Integer;
begin
try
SavingStream.ReadBuffer(i,SizeOf(i));
SetLength(Categories,i);
for i:=0 to Length(Categories)-1 do
   begin
   SavingStream.ReadBuffer(Categories[i].Name,SizeOf(Categories[i].Name));     
   SavingStream.ReadBuffer(Categories[i].ID,SizeOf(Categories[i].ID));         
   SavingStream.ReadBuffer(Categories[i].Default,SizeOf(Categories[i].Default));
   SavingStream.ReadBuffer(j,SizeOf(j));
   SetLength(Categories[i].ChildrenType,j);
   if j>=1 then for j:=0 to Length(Categories[i].ChildrenType)-1 do SavingStream.ReadBuffer(Categories[i].ChildrenType[j],SizeOf(Categories[i].ChildrenType[j]));
   end;
finally
SavingStream.Free;
end;

主要问题之一是我不完全理解这种方法背后的逻辑。据我了解，SizeOf(i) 基本上是说获取同质文件的某一部分并将其作为变量的值。但是如何存储大小可变的字符串和数组呢？我知道可以限制记录本身的大小，但是我不想限制某些字符串变量。

因此，我需要您的建议，我使用的方法是否有效，以及如何使其在我的具体情况下发挥作用。也许有更好的方法来存储这些信息？请记住，我必须存储各种不同类型，包括图像。

提前谢谢。

Answer 1

您需要将可变长度数据（例如字符串）序列化为不包含任何指向其他内存地址的指针的平面格式。

尝试这样的事情：

procedure WriteIntegerToStream(Stream: TStream; Value: Integer);
begin
  Stream.WriteBuffer(Value, Sizeof(Value));
end;

procedure WriteBooleanToStream(Stream: TStream; Value: Boolean);
begin
  Stream.WriteBuffer(Value, Sizeof(Value));
end;

procedure WriteStringToStream(Stream: TStream; const Value: String);
var
  S: UTF8String;
  Len: Integer;
begin
  S := UTF8String(Value);
  Len := Length(S);
  WriteIntegerToStream(Stream, Len);
  Stream.WriteBuffer(PAnsiChar(S)^, Len);
end;

var 
  SavingStream: TFileStream;
  i, j: Integer;
begin
  SavingStream := TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
  try
    WriteIntegerToStream(SavingStream, Length(Categories));
    for i := 0 to Length(Categories)-1 do
    begin         
      WriteStringToStream(SavingStream, Categories[i].Name);
      WriteIntegerToStream(SavingStream, Categories[i].ID);
      WriteBooleanToStream(SavingStream, Categories[i].Default);
      WriteIntegerToStream(SavingStream, Length(Categories[i].ChildrenType));
      for j := 0 to Length(Categories[i].ChildrenType)-1 do
      begin
        // write ChildrenType[j] data to SavingStream as needed...
      end;
  finally
    SavingStream.Free;
  end;
end;

然后你可以在读回文件时执行类似的操作：

function ReadIntegerFromStream(Stream: TStream): Integer;
begin
  Stream.ReadBuffer(Result, Sizeof(Result));
end;

function ReadBooleanFromStream(Stream: TStream): Boolean;
begin
  Stream.ReadBuffer(Result, Sizeof(Result));
end;

function ReadStringFromStream(Stream: TStream): String;
var
  S: UTF8String;
  Len: Integer;
begin
  Len := ReadIntegerFromStream(Stream);
  SetLength(S, Len);
  Stream.ReadBuffer(PAnsiChar(S)^, Len);
  Result := String(S);
end;

var 
  LoadingStream: TFileStream;
  i, j: Integer;
begin
  LoadingStream := TFileStream.Create('SAVE.test', fmOpenRead or fmShareDenyWrite);
  try
    i := ReadIntegerFromStream(LoadingStream);
    SetLength(Categories, i);
    for i := 0 to Length(Categories)-1 do
    begin
      Categories[i].Name := ReadStringFromStream(LoadingStream);
      Categories[i].ID := ReadIntegerFromStream(LoadingStream);
      Categories[i].Default := ReadBooleanFromStream(LoadingStream);
      j := ReadIntegerFromStream(LoadingStream);
      SetLength(Categories[i].ChildrenType, j);
      for j := 0 to Length(Categories[i].ChildrenType)-1 do
      begin
        // read ChildrenType[j] data from LoadingStream as needed...
      end;
    end;
  finally
    LoadingStream.Free;
  end;
end;