I wrote a simple code to open plain text file with Qt 5's QFile as seen below;
// main.cpp
#include <iostream>
using std::endl;
using std::cout;
#include <QCoreApplication>
#include <QFile>
#include <QIODevice>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QFile plainFile("plain.txt");
if(plainFile.open(QIODevice::ReadOnly | QIODevice::Text))
{
cout << "File opened successfull" << endl;
plainFile.close();
}
else{
cout << "could not open file." << endl;
}
return a.exec();
}
The output when compiled and run is "could not open file".
What am I do wrong?
Probably because plain.txt does not exist in the current working directory or in the PATH. Make sure the file is in the working directory or pass the absolute path to QFile.
Also see what QFile::exists returns.
Wouter Huysentruit is right.
Remember, that, by default, when you running application from QtCreator working directory is, for example, C:\Projects\build-Test-Desktop_Qt_5_1_0_MinGW_32bit-Debug. But your .exe file lay in C:\Projects\build-Test-Desktop_Qt_5_1_0_MinGW_32bit-Debug\Debug.
When you run your .exe directly, then working directory will be that folder, where this file is layed now.
So, you can:
1.Pass absolute path.
2.Put file in current working directory (I suppose that it is best solution).
3.Just change relative path: QFile plainFile("debug/plain.txt");
Related
It's strange, I add desired file into the resources via Add Existing Files..., the file is there. I run qmake ("Build->Run qmake") to make the file available.
The first issue: I can't write anything into the file from output terminal! But when I manually write into the file, the output terminal shows the change every time I run it. Second issue: it still says QIODevice::read: device not open !
Here's my code:
#include <QCoreApplication>
#include <QDebug>
#include <QFile>
#include <QString>
#include <QTextStream>
#include <iostream>
void wFile(QString Filename)
{
QFile nFile(Filename);
QTextStream str(&nFile);
qDebug() << "what do you want to write in the desired file: ";
str.readLine();
if (!nFile.open(QFile::WriteOnly | QFile::Text))
{
qDebug() << "could not open the file";
return;
}
nFile.flush();
nFile.close();
}
void read (QString Filename){
QFile nFile(Filename);
if(!nFile.open(QFile::ReadOnly | QFile::Text))
{
qDebug() << "could not open file for reading";
return;
}
QTextStream in(&nFile);
QString nText = in.readAll();
qDebug() << nText;
nFile.close();
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QString nFilename =":/MyFiles/DocumentArminV.txt";
wFile(nFilename);
read(nFilename);
return a.exec();
}
And here's output terminal of the code:
The files saved in a qresource are read-only since they are part of the executable so you can not write or modify them.
docs:
Currently, Qt always stores the data directly in the executable, even on Windows, macOS, and iOS, where the operating system provides native support for resources. ...
It's strange, I add desired file into the resources via Add Existing Files..., the file is there. I run qmake ("Build->Run qmake") to make the file available.
The first issue: I can't write anything into the file from output terminal! But when I manually write into the file, the output terminal shows the change every time I run it. Second issue: it still says QIODevice::read: device not open !
Here's my code:
#include <QCoreApplication>
#include <QDebug>
#include <QFile>
#include <QString>
#include <QTextStream>
#include <iostream>
void wFile(QString Filename)
{
QFile nFile(Filename);
QTextStream str(&nFile);
qDebug() << "what do you want to write in the desired file: ";
str.readLine();
if (!nFile.open(QFile::WriteOnly | QFile::Text))
{
qDebug() << "could not open the file";
return;
}
nFile.flush();
nFile.close();
}
void read (QString Filename){
QFile nFile(Filename);
if(!nFile.open(QFile::ReadOnly | QFile::Text))
{
qDebug() << "could not open file for reading";
return;
}
QTextStream in(&nFile);
QString nText = in.readAll();
qDebug() << nText;
nFile.close();
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QString nFilename =":/MyFiles/DocumentArminV.txt";
wFile(nFilename);
read(nFilename);
return a.exec();
}
And here's output terminal of the code:
The files saved in a qresource are read-only since they are part of the executable so you can not write or modify them.
docs:
Currently, Qt always stores the data directly in the executable, even on Windows, macOS, and iOS, where the operating system provides native support for resources. ...
It's strange, I add desired file into the resources via Add Existing Files..., the file is there. I run qmake ("Build->Run qmake") to make the file available.
The first issue: I can't write anything into the file from output terminal! But when I manually write into the file, the output terminal shows the change every time I run it. Second issue: it still says QIODevice::read: device not open !
Here's my code:
#include <QCoreApplication>
#include <QDebug>
#include <QFile>
#include <QString>
#include <QTextStream>
#include <iostream>
void wFile(QString Filename)
{
QFile nFile(Filename);
QTextStream str(&nFile);
qDebug() << "what do you want to write in the desired file: ";
str.readLine();
if (!nFile.open(QFile::WriteOnly | QFile::Text))
{
qDebug() << "could not open the file";
return;
}
nFile.flush();
nFile.close();
}
void read (QString Filename){
QFile nFile(Filename);
if(!nFile.open(QFile::ReadOnly | QFile::Text))
{
qDebug() << "could not open file for reading";
return;
}
QTextStream in(&nFile);
QString nText = in.readAll();
qDebug() << nText;
nFile.close();
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QString nFilename =":/MyFiles/DocumentArminV.txt";
wFile(nFilename);
read(nFilename);
return a.exec();
}
And here's output terminal of the code:
The files saved in a qresource are read-only since they are part of the executable so you can not write or modify them.
docs:
Currently, Qt always stores the data directly in the executable, even on Windows, macOS, and iOS, where the operating system provides native support for resources. ...
I have text files in my resource file and I'd like to be able to provide a path for this file to std::ifstream. Neither :\file_name.txt nor ..\file_name.txt works.
Does anyone know how to fix it?
Qt resource files are not filesystem files. Those files are loaded in memory as static char arrays. You can see for yourself looking in your build directory for qrc_*.cpp files. You can get data from there if you want, or you might want to use QTextStream for reading those, using the QIODevice constructor with a QFile.
You don't specify what you want to do exactly, but this is a sample that reads what is inside the file:
#include <QtCore/QCoreApplication>
#include <QTextStream>
#include <QFile>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QFile file(":/test.txt");
QTextStream stream(&file);
if (!file.open(QIODevice::ReadOnly)) {
qFatal("Failed to open file.");
return -1;
}
QString text = stream.readAll();
if (text.isNull()) {
qDebug("Failed to read file.");
return -1;
}
qDebug("File content is: %s. Bye bye.", qPrintable(text));
return 0;
}
I am trying to do console application to read pixels from image:
#include <QtCore/QCoreApplication>
#include <QtGui/QImage>
#include <iostream>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QImage *img = new QImage("adadad.jpg");
//std::cout << "Type filename:" << std::endl;
img->isNull();
return a.exec();
}
That doesn't work I got: (IT doesn't compile, but anyway file isn't exist yet...)
File not found: tmp/obj/debug_shared/main.o:: In function `main':
What is going on? Is it impossible to use Qimage with console app?!
EDIT:
screen
It is possible to use QImage in a console application, you must make sure that QtGui is configured though. If you chose a console app, your .pro file might contain something like
CONFIG += console
QT -= gui
If that's the case, remove the QT -= gui line.
QImage("adadad.jpg");
Will probably look for a file called adadad.jpg on the current working directory for your application. Check if that file is present. Otherwise, use a fully qualified path.
img->isNull() doesn't do anything on it's own, try this instead:
if(img->isNull())
std::cout << "Image isNull!\n";
else
std::cout << "Image loaded\n";
My guess is that the local directory of the executable is not the same as the location of that image, so Qt can't find the file. Try specifying the complete path.
EDIT: Ahh... didn't realize it was a compilation problem. That looks suspiciously like a moc issue. What build system are you using? and can you confirm that the moc step is executing?
This modification of your code will compile and run as expected if there is a valid image file in the current working directory when you run the app. It will display Image loaded
#include <QtGui/QImage>
#include <iostream>
int main(int argc, char *argv[])
{
QImage *img = new QImage("adadad.jpg");
if(img->isNull())
std::cout << "Image is null";
else
std::cout << "Image loaded";
return 0;
}
You do not need to create an instance of QCoreApplication unless you have subclassed it and put your program code in that subclass.
Update:
Your program does not exit so you are probably getting that compile error because it can't replace the executable because it is still running (and locked). The file locking is more likely to be an issue under Windows.
An important note when you are loading a file using directly "adadad.jpg" in your code. Even if you put the file inside the debug/release folder, QImage will always be null if loaded this way.
I run into this problem yesterday and I fixed it by using the Qt library to get the full path: QCoreApplication::applicationDirPath().
There is two way to achieve that, first one is when you create the img object.
QImage img( QCoreApplication::applicationDirPath() + "adadad.jpg");
if( img.isNull())
{
qDebug() << "Loading Error - file: adadad.jpg.";
return false;
}
or using the load function
QImage img;
if( !img.load(QCoreApplication::applicationDirPath() + "adadad.jpg"))
{
qDebug() << "Loading Error - file: adadad.jpg.";
return false;
}