MEMORYSTREAM问题，读不到数据。

Question

做一个文件修复函数，从文件名，查找字符，比对，再替换字符。但是在ARRAY OF CHAR遇到问题，如果手动设置数组，READBUFFER可以读到数据，替换也正常。现在用动态数组做动态列表修复，但是SetLength(CmpStr,RepairStrLen)后，SIZEOF(CmpStr)值永远为4，而且读取不到数据。全部家当送上function TMainFrm.RepairStr(sFileName:String;FindStr:string;RepairStr:String;RepairStrLen:integer):Boolean;
var
  TmpMemoryStream : TMemoryStream;
  CmpStr        : array of Char;
  CmpStr1        : array of Char;
  FileSize,iAddress      : Integer;
  bWrite        : Boolean;
  s          : String;
  I        : Integer;
begin
  bWrite := False;
  Result := False;
  try
    TmpMemoryStream := TMemoryStream.Create;
    try
      TmpMemoryStream.Clear;
      TmpMemoryStream.LoadFromFile(sFileName);
      FileSize := TmpMemoryStream.Size;
      TmpMemoryStream.Position:=TmpMemoryStream.Size;
      TmpMemoryStream.Position:=0;
      SetLength(CmpStr,RepairStrLen);
      SetLength(CmpStr1,RepairStrLen);
      SetLength(s,FileSize);
      CopyMemory(@s[1],TmpMemoryStream.Memory,TmpMemoryStream.size);
      iAddress := Pos(FindStr,s) - 1;
      TmpMemoryStream.Seek(iAddress,0);
      TmpMemoryStream.ReadBuffer(CmpStr, SizeOf(CmpStr));
      TmpMemoryStream.Seek(iAddress,0);
      TmpMemoryStream.ReadBuffer(CmpStr1, SizeOf(CmpStr1));
      TmpMemoryStream.Seek(iAddress,0);
      For I := 0 to RepairStrLen do
      begin
        if CmpStr[I] <> RepairStr[I+1] then
          CmpStr[I] := RepairStr[I+1];
      end;
      if string(CmpStr) <> string(CmpStr1) then
      begin
        TmpMemoryStream.WriteBuffer(CmpStr, SizeOf(CmpStr));
        bWrite := True;
      end;
    Finally
      Result := True;
      if bWrite = True then
        TmpMemoryStream.SaveToFile(sFileName);
      TmpMemoryStream.Free;
    end;
  except
    TmpMemoryStream.Free;
    Result := False;
    exit;
  end;
end;

Answer 1

SIZEOF(CmpStr)
改为
Length(CmpStr)

Answer 2

SIZEOF(CmpStr) 
指针在32位系统中占用的长度就是4

Answer 3

CmpStr 是数组,不是指针,俩回事 

Answer 4

数组是可以SIZEOF的，我搞不明白为什么动态数组为什么不能SIZEOF

Answer 5

SizeOf(array)
编译器在编译时候，就判断变量类型，将结果，也就是立即数４编译进指令。
Length(array)调用下面方法取动态数组长度procedure   _DynArrayLength;   
  asm   
         TEST         EAX,EAX   
         JZ             @@skip   
         MOV           EAX,[EAX-4]   //数组头地址-4的地址中的内容（即动态数组长度）取出
  @@skip:   
  end;   

Answer 6

还有一种取动态数组长度的方法，这种更容易理解。
var
    axt: array of byte;
    P: PInteger;
begin
    SetLength(axt, 20);    P := PInteger(axt);
    dec(P);
    si := P^;
    ShowMessage(IntToStr(P^));
end;

Answer 7

TmpMemoryStream.ReadBuffer(@CmpStr[1], Length(CmpStr));

Answer 8

这是无法使用指针啊。[Error] MainForm.pas(269): Constant object cannot be passed as var parameter

Answer 9

function TMainFrm.RepairStr(sFileName:String;FindStr:string;RepairStr:String;RepairStrLen:integer):Boolean;
var
  TmpMemoryStream : TMemoryStream;
  CmpStr        : array of Char;
  CmpStr1        : array of Char;
  FileSize,iAddress,SizeOf1      : Integer;
  bWrite        : Boolean;
  s          : String;
  I        : Integer;
begin
  bWrite := False;
  Result := False;
  SetLength(CmpStr,RepairStrLen);
  SetLength(CmpStr1,RepairStrLen);
  try
    TmpMemoryStream := TMemoryStream.Create;
    try
      TmpMemoryStream.Clear;
      TmpMemoryStream.LoadFromFile(sFileName);
      FileSize := TmpMemoryStream.Size;
      TmpMemoryStream.Position:=TmpMemoryStream.Size;
      TmpMemoryStream.Position:=0;
      SetLength(s,FileSize);
      CopyMemory(@s[1],TmpMemoryStream.Memory,TmpMemoryStream.size);
      iAddress := Pos(FindStr,s) - 1;
      if iAddress >= 0 then
      begin
        TmpMemoryStream.Seek(iAddress,0);
        TmpMemoryStream.ReadBuffer(CmpStr[0],Length(CmpStr));
        TmpMemoryStream.Seek(iAddress,0);
        TmpMemoryStream.ReadBuffer(CmpStr1[0],Length(CmpStr1));
        TmpMemoryStream.Seek(iAddress,0);
        For I := 0 to RepairStrLen - 1 do
        begin
          if CmpStr[I] <> RepairStr[I + 1] then
            CmpStr[I] := RepairStr[I + 1];
        end;
        if string(CmpStr) <> string(CmpStr1) then
        begin
          TmpMemoryStream.WriteBuffer(CmpStr[0], Length(CmpStr));
          bWrite := True;
        end;
      end;
    Finally
      Result := True;
      if bWrite = True then
        TmpMemoryStream.SaveToFile(sFileName);
      TmpMemoryStream.Free;
    end;
  except
    Result := False;
    exit;
  end;
end;已经解决，结帖。

Answer 10

TmpMemoryStream.ReadBuffer(CmpStr[0], Length(CmpStr));
你可以看下TCustomMemoryStream.Read的实现,最后调用的是Move(Pointer(Longint(FMemory) + FPosition)^, Buffer, Result);
而move的实现procedure       Move( const Source; var Dest; count : Integer );
{$IFDEF PUREPASCAL}
var
  S, D: PChar;
  I: Integer;
begin
  S := PChar(@Source);
  D := PChar(@Dest);
  if S = D then Exit;
  if Cardinal(D) > Cardinal(S) then
    for I := count-1 downto 0 do
      D[I] := S[I]
  else
    for I := 0 to count-1 do
      D[I] := S[I];
end;
 注意D := PChar(@Dest);这句,move会自己去取地址,所以如果你送给ReadBuffer的第一个参数已经是个地址了,这里就会出错