QDataStream reading into QString

I'm trying to learn how to use QDataStream for serializing my data and then read it out again later. However, I'm having a trouble with reading out a QString.

The code is just "Hello World" type of app that is just used to see how things work instead of doing anything actually useful.

Code:

---

QFile outFile( "output.txt" );
   outFile.open( IO_WriteOnly );
 
   QDataStream outStream( &outFile );
 
   outStream << "The beginning of a series of numbers";
 
   for (int i = 0; i < 50000; i++)
   {
 
      outStream << (Q_INT32) i;
 
   }/* end loop through numbers */
 
   double outFloat = 3.1516342315;
 
   double* addressOfFloat = &outFloat;
 
   outStream << outFloat;
 
   outStream << "The end of the series of numbers.  Have a nice day.";
 
   outFile.close( );

---

Opening up the binary file, everything looks to be in there correctly. The strings show up along with the binary for all of the numbers.

Reading out, however, is a different issue.

Code:

---

QFile inFile( "output.txt" );
   inFile.open( IO_ReadOnly );
   QDataStream inStream( &inFile );
 
   Q_INT32 data[50000];
 
   QString string;
 
   inStream >> string;
 
   for (int i = 0; i < 50000; i++)
   {
 
      inStream >> data[i];
 
    }
 
   double doubleCheck;
   inStream >> doubleCheck;
 
   inStream >> string;
 
   inFile.close();

---

When I take a look at the strings that were read in, it shows up as a string of ??'s instead of the string that I output. This occurs the same whether I'm on Sun or Windows. Am I forgetting some function call?

Thanks in advance for any help.

what strings actually insteads?

You did not write a QString but instead a

Code:

---

const char *

---

This

Code:

---

outStream << QString("The beginning of a series of numbers");

---

should work. Or you could change the type you are trying to read out of the stream.

Quote:

---

Originally Posted by Codepoet

You did not write a QString but instead a

Code:

---

const char *

---

This

Code:

---

outStream << QString("The beginning of a series of numbers");

---

should work. Or you could change the type you are trying to read out of the stream.

---

This worked just fine. It's interesting that they didn't mention this in the example that trolltech has in the 3.3 documentation for QDataStream.

http://doc.trolltech.com/3.3/qdatastream.html#details

Quote:

---

Originally Posted by Docs

Example (write binary data to a stream):

QFile file( "file.dat" );
file.open( IO_WriteOnly );
QDataStream stream( &file ); // we will serialize the data into the file
stream << "the answer is"; // serialize a string
stream << (Q_INT32)42; // serialize an integer


Example (read binary data from a stream):

QFile file( "file.dat" );
file.open( IO_ReadOnly );
QDataStream stream( &file ); // read the data serialized from the file
QString str;
Q_INT32 a;
stream >> str >> a; // extract "the answer is" and 42

---

The QDataStream allows you to serialize some of the Qt data types. For QString, char pointer is right. These are my example:
First is used to write a QString into a file:

Code:

---

QFile file("file.dat");
                    file.open(QIODevice::WriteOnly);
                    QDataStream out(&file);
    	    out << "Hello World!";

---

Second is used to read content from a file:

Code:

---

char *ch;
	    QFile file("file.dat");
                    file.open(QIODevice::ReadOnly);
                    QDataStream in(&file);
    	    in >> ch;
                    QString str(ch);

---

The "str" is your result!