How we can open a png file with QFile and then save it with new name......

stackprogramer

How we can open a png file with QFile and then save it with new name......
for file text i had not any problem but for binary file it can not read all data corecty.........
for example for read a png file i read.......

  QByteArray binaryFile= file.readAll();

 QString SerialOutputFile;


                   if(ui->lineEditSerialOutputDirectory->text().isEmpty()) {
                       SerialOutputFile =QDir::currentPath()+"/SerialOutputFile.png";

                   }else{
                       SerialOutputFile =ui->lineEditSerialOutputDirectory->text()+"/SerialOutputFile.png";
                   }
                 //QString SerialOutputFile =QDir::currentPath()+"SerialOutputFile.png";
                 QFile outputFile(SerialOutputFile);
                 outputFile.open(QIODevice::WriteOnly);
                 QString str =binaryFile;

                 if(!outputFile.isOpen())
                 {
                     //alert that file did not open
                 }

                 QTextStream outStream(&outputFile);

                 outStream << str;

                 outputFile.close();
                binaryFile.clear();

               //open text file to user
                 QDesktopServices::openUrl(QUrl(SerialOutputFile));

output only is...........but png is 4kbyte...........

?PNG

J.Hilk

@stackprogramer
your problem is probably here:
QTextStream outStream(&outputFile);

QTextstream expects text comfort chars Use a QDataStream instead.

That said, did you know about QFiles static

functions ?
https://doc.qt.io/qt-5/qfile.html#rename-1
https://doc.qt.io/qt-5/qfile.html#copy-1

which can both be used to rename a file

stackprogramer

@J-Hilk
I used QDatastream but......size of input png is 4564byte and output is 4568....
png file is not open..........my main problem is open png file....... png not show


 
                  if (!file.open(QIODevice::ReadOnly)) {
                      qDebug() << file.errorString();
                  }
                

                   QByteArray binaryFile= file.readAll();
                   qDebug()<<binaryFile.size();
                
                

                   QString SerialOutputFile;


                   if(ui->lineEditSerialOutputDirectory->text().isEmpty()) {
                       SerialOutputFile =QDir::currentPath()+"/SerialOutputFile.png";

                   }else{
                       SerialOutputFile =ui->lineEditSerialOutputDirectory->text()+"/SerialOutputFile.png";
                   }
                 //QString SerialOutputFile =QDir::currentPath()+"SerialOutputFile.txt";
                 QFile outputFile(SerialOutputFile);
                 outputFile.open(QIODevice::WriteOnly);
                 QString str =binaryFile;

                 if(!outputFile.isOpen())
                 {
                     //alert that file did not open
                 }

                 QDataStream outStream(&outputFile);

                 outStream << binaryFile;

                 outputFile.close();
                binaryFile.clear();

               //open text file to user
                 QDesktopServices::openUrl(QUrl(SerialOutputFile));
                 qDebug()<<outputFile.size();

stackprogramer

I found solution my problem is solved.......
Problem: QDataStream uses the "<<" method to write data with extra characters, such as hexadecimal notation "0000 001a"
Solution: QDataStream uses writeRawData() to write data to avoid extra bytes.
more info https://www.programmersought.com/article/1716209297/

QFile file("file.txt");
  file.open(QIODevice::WriteOnly);
  QDataStream out(&file);   // we will serialize the data into the file
  
  / / original code
  / / Use the operator input will make out with invalid characters, the output is 30
  //out << QString("the answer is");   // serialize a string
  
  / / changed code
  / / Output results are 14, no invalid characters
  out.writeRawData("the answer is",sizeof("the answer is"));

  qDebug()<<"length : "<<file.size();
  file.close();
  exit(1);

JonB

@stackprogramer

How we can open a png file with QFile and then save it with new name

I don't understand why you are using stream anything, if all you are doing is calling writeRawData().

To write raw bytes straight to a file opened with QFile you can just use QIODevice::write.

But if you are just copying a png file to a new name, as your question states, then @J-Hilk 's [static]bool QFile::copy(const QString &fileName, const QString &newName) is as simple & efficient as it gets....