fstream unix problem in reading

I am trying to read from binary file on UNIX. The file exists and has several data information in it.

The code looks like this:

开发者_开发技巧fstrean fstrHandler;

string strFileName;

char Buf[30000];

fstrHandler.open(strFileName.c_str(), ios::in | ios::binary);

fstrHandler.seekp(0, std::ios_base::beg);

std::cout<< "Posi before read= "<< fstrHandler.tellg()<<endl; //*** Show after running 0

fstrHandler.read (Buf, 400);

std::cout<< "Posi after read= "<< fstrHandler.tellg()<<endl; //*** Show after running 0

std::cout<< " gcount ()= "<< fstrHandler.gcount ()<< << endl; //*** Show after running 0

if (fstrHandler.eof ()) {
       fstrHandler.clear();
}

After the read I get that the position in file is still zero zero, but the file is not empty.

Try seekg rather than seekp, and is there 400 bytes in the file? this appears to work okay for me, if you input a file that contains more than 400 bytes. If less, then the tellg after read reports -1, but gcount() is correct.

Also, after opening the file - test to see if the file was indeed opened e.g.

if (fstrHandler)
{
// do stuff
}
else
  std::cerr << "foo bar" << std::endl;