readfile的使用

Question

我想要从一个文件中 读出标准头32字节
 为何出错了!
 代码如下:
const SIGNNAME_LENGTH=32;nReal:Longint;
b:Cardinal;
SignName: array [0..SIGNNAME_LENGTH-1] of byte;
 
b:=ReadFile(hFile,@SignName,SIGNNAME_LENGTH,@nReal,nil); //(出错行,hfile是createfile的返回)

Answer 1

提示出错:constant object cannot be passed as var parameter

Answer 2

function ReadFile(hFile: THandle; var Buffer; nNumberOfBytesToRead: DWORD;
  var lpNumberOfBytesRead: DWORD; lpOverlapped: POverlapped): BOOL; stdcall;
http://www.emutalk.net/archive/index.php/t-4009.htmlCybermanApril 7th, 2002, 04:44
Originally posted by Mayco 
I have a problem: when I use the readfile api function in delphi it returns everything what i need except the first byte (when the file begins with "123..." it just returns "23...").This is the piece of code I use:procedure openfile();
var
dwread:LongWord;
hFile: THandle;
data: Shortstring;
begin 
hFile := createfile(PChar('c:\file.bin'), GENERIC_READ, FILE_SHARE, nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL + FILE_FLAG_RANDOM_ACCES, 0);
SetFilePointer(hFile, 0, nil, FILE_BEGIN);
Readfile(hFile, data, 64, dwread, nil);
Closehandle(hFile);
end;c:\file.bin is the file I want to read of course.
data must contain the first 64 bytes of a binary file but it doesn't add the first byte. 
I suggest not setting the file pointer the first time by commenting it out. Then run the code. Also if you have a 'file' position function I would dump that information to a debug text object in some window of your application. Useful for figuring out such things.Cyb

Answer 3

你没看人家的例子？
ReadFile前先用SetFilePointer，你引用参数又不正确，将@SignName,@nReal的@去掉

Answer 4

看过了!我的代码如下,在编译时不通过
var
Result: Longint;
bKernelExist,nStrategyCount,nKernelStrategyCount: Longint;
reportFlow:array [0..8191] of byte;
pReportFlow:PByte;
nDefaultStrategyCookie: Longint;
Password:array [0..6] of byte;
pPassword:PByte;
pParamCheck:Longint;
hFile:Integer;
nFlowID:Longint;
pBuf,pBufTemp:PByte;
i:Integer;
pTEFSInfoFlowLen:Longint;
nFileSize,nReal,b:Longint;
SignName: array [0..SIGNNAME_LENGTH-1] of byte;
pSignName:pchar;
begin
    OpenDialog1.Execute;
    if trim(OpenDialog1.FileName)<>'' then begin
        showmessage(OpenDialog1.FileName);
        result:=DSF_Driver_FileCanServe(pchar(OpenDialog1.FileName));
        if result<>1 then exit;
        hFile:=DSF_Driver_CreateFile(pParamCheck,pchar(OpenDialog1.FileName),GENERIC_READ or GENERIC_WRITE, 0, nil, OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL, 0);
        nFileSize:= GetFileSize(hfile,nil);
        if (nFileSize=0) and ((nFileSize mod TEFS_ALIGN_CONST)<>0) then exit;//不为0,或是不是256的倍数,一定不是加密文件
        //加密文件的尾部是配置块,配置块的最后32字节是签名
         b:=SetFilePointer(hFile,-SIGNNAME_LENGTH,nil,FILE_END); //seek到要求的位置
         if (b<>(nFileSize-SIGNNAME_LENGTH)) then begin CloseHandle(hFile);exit;end;  //出错
        //读出标准头32字节
        b:=ReadFile(hFile,SignName,SIGNNAME_LENGTH,nReal,nil); //从原文件中读      end;

Answer 5

ReadFile返回的是Boolean型，nReal改成DWORD,这才是一直不能编译的原因。我的测试代码：
const SIGNNAME_LENGTH=32;
var
  SignName: array [0..SIGNNAME_LENGTH-1] of byte;
  hFile:THandle;
  nReal:DWORD;
  i:integer;
  Result:string;
begin
  hFile:=CreateFile(PChar('c:\1.mp3'),GENERIC_READ,FILE_SHARE_READ,nil,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL ,0);
 if ReadFile(hFile,SignName,SIGNNAME_LENGTH,nReal,nil) then;
  for i:=0 to SIGNNAME_LENGTH-1 do
   Result:=Result+Format('%2.2x ',[SignName[i]]);
   ShowMessage(Result);
end;