C ++ file stream objects

likang1986

Use the same file stream object ifstream in_stream; to open multiple files, open one after reading it, then close it, and then use it to open the other, close, and fail when opening to the third file, why?

珈蓝易拉罐

Post the code, it should not.

superandy

The state of the stream object is retained internally, and you may need to call the clear, seek, ingor and other interfaces to reset the state.

It's better not to reuse variables.

likang1986

Code:
 ifstream in_stream;

  in_stream.open ("stock library.txt");
  if (in_stream.fail ())
  {
      cout << "Opening file fail 1111!" << endl;
      exit (1); // Exit abnormally
  }

  string strtemp;
  int i;
  
  string strGoodsName; // Item name
  string strModelNum; // Product model
  string strGoodsNum; // Article number
  int nCount; // Number of products
  double dwPrice; // commodity purchase price (unit price)
  double dwProfits; // commodity profit ()
  string strProvider; // provider
  string strManName; // Operator
  
  // The following is the initial purchase warehouse
  in_stream.seekg (0, ios :: beg);

  for (i = 0; i <8; i ++)
in_stream >> strtemp; // Ignore the first line
  for (i = 0; i <12; i ++) // Read the content formally
  {
in_stream >> strGoodsName >> strModelNum >> strGoodsNum >> nCount >> dwPrice
>> dwProfits >> strProvider >> strManName;

m_InWareHouse.Add (CMerchandise (strGoodsName, strModelNum, strGoodsNum, nCount,
dwPrice, dwProfits, strProvider, strManName));
  }

  in_stream.close ();

  // The following is the initialization inventory
  in_stream.open ("Inventory.txt");
  if (in_stream.fail ())
  {
      cout << "Opening file fail 2222!" << endl;
      exit (1); // Exit abnormally
  }
  
  in_stream.seekg (0, ios :: beg);

  for (i = 0; i <7; i ++)
in_stream >> strtemp; // Ignore the first line

   for (i = 0; i <12; i ++) // Read the content formally
  {
in_stream >> strGoodsName >> strModelNum >> strGoodsNum >> nCount >> dwPrice
>> dwProfits >> strProvider;

m_InWareHouse.Add (CMerchandise (strGoodsName, strModelNum, strGoodsNum, nCount,
dwPrice, dwProfits, strProvider, ""));
  }

  in_stream.close ();

  // The following is the initialization sales library
  
   in_stream.open ("sales library.txt");

  if (in_stream.fail ())
  {
   cout << "Opening file fail 3333!" << endl;
      exit (1); // Exit abnormally
  }

  in_stream.seekg (0, ios :: beg);

  for (i = 0; i <7; i ++)
in_stream >> strtemp; // Ignore the first line

   for (i = 0; i <12; i ++) // Read the content formally
  {
in_stream >> strGoodsName >> strModelNum >> strGoodsNum >> nCount >> dwPrice
>> dwProfits >> strProvider;

m_InWareHouse.Add (CMerchandise (strGoodsName, strModelNum, strGoodsNum, nCount,
dwPrice, dwProfits, strProvider, ""));
  }

   in_stream.close ();
  
The basic code is the above, and the result is "Opening file fail 3333!"

firegun

Agreesuperandy
Add a sentence after close:
in_stream.clear ();
Clear all status flags

in_stream.fail () returns true, indicating that a failbit or badbit is set. And when in_stream reads
End-of-file will set up eofbit and failbit at the same time

xxmoto619

It turned out to be like this, I understand. I also encountered this problem, and I still don't understand it. Experiment.