Problem with ifstream and Qt Creator

SGaist

Hi,

You should run the debugger on your application to see exactly where it fails and get a stack trace.

That said, you're doing some dangerous assumptions in your code. You are allocating an arbitrary big chunk of memory while reading some dynamically changing number of bytes.

Then you generate a vector (std::vector ?) from that data by passing the start and end addresses of buffer to the constructor which make think that you wanted to use the iterator based constructor.

BadHombre

So i debugged the code and tried to step in at the Position where it fails ... but i can't step in so the Problem seems to be

 char * buffer = new char [size];

but how could it be that it works on visual studio and crashed on qt creator ? :/
Do you have maybe an idea what i can do now ?

BadHombre

In the second example where i tried to create the vector it creash at the position

[[noreturn]] void _Xlen() const
		{	// report a length_error
		_Xlength_error("vector<T> too long");
		}

ambershark

@BadHombre What is the value of size when it crashes?

Is your Qt Creator using mingw or visual c++ for it's compiler? That could make all the difference. VS may handle weird size cases like -1 or 0 whereas mingw may not. Neither of those are valid and visual studio may just be ok with that. VS tends to be pretty loose in conforming to standards.

BadHombre

@ambershark size is an integer and is the number of chars i need to store the elements from the File in the buffer. Its sth like 6000.
My Qt Creator is using Desktop QT 5.7.1 MSVC 2015_64 bit.

ambershark

@BadHombre Ok let's take std c++ out of it and use Qt.. This is the Qt forum after all.

Change your file reading code to:

QFile f("myfile");
QByteArray fileData;
if (f.open(QIODevice::ReadOnly))
{
   fileData = f.readAll();
}

Another thing you could do is throw it in the debugger and show us the backtrace output.

jsulm

@BadHombre said in Problem with ifstream and Qt Creator:

Its sth like 6000

Did you really check the value of size? That's what a debugger is for.
Are you sure your app crashes exactly at "char * buffer = new char [size];"?
Also you do not seek to the beginning of the file before reading from it!

file.seekg(0, std::ios::end);
int size = file.tellg();
char * buffer = new char [100000000]; // muss geändert werden
file.read(buffer, size);

BadHombre

@jsulm You're right i get an wrong size ... i used now qDebug()<< size and it prints -1 ... but why ... in Visual Studio its working ....

char * buffer;
	long size;
	file.seekg(0, std::ios::end);
	size = file.tellg();
	file.seekg(0, std::ios::beg);
	buffer = new char[size];
	file.read(buffer, size);
	file.close();

	double* double_values = (double*)buffer;//reinterpret as doubles
	vector<double> buffer2(double_values, double_values + (size / sizeof(double)));

jsulm

@BadHombre First, you should check whether file was opened:

ifstream file("fileName", ios::in | ios::binary | ios::ate);
if (file) {
...
}

BadHombre

@jsulm it doesn t open the file ... but i checked also the file name and its correct. The .bin file should also be right because with visual studio it works ...

QStringList Filename = QFileDialog::getOpenFileNames(
        this,
        tr("Choose your File"),
        "C://",
        "All files (*.*);;BIN (*.bin)");

@ambershark sorry i didn 't saw your post i will try it.

BadHombre

@ambershark it doesn ' open the file ... so it should be sth wrong with the path... I printed the Filename which i get with Qstringlist and it looks like that :

("E:/test/file.bin")

jsulm

@BadHombre You should try to remove ios::ate as it is for output but you're opening for reading (ios::in).
Also I'm not sure ifstream supports / in paths on Windows (Qt does). Try to replace / with \\.
From here: http://www.cplusplus.com/reference/fstream/ifstream/ifstream/
"filename
A string representing the name of the file to open.
Specifics about its format and validity depend on the library implementation and running environment."

tham

Could you show us your .pro file(minimum one please)?Which version of Qt, QtCreator your are using?Are you sure you are using the same compiler to compile your codes?

Besides, you do not need to use raw pointer, there are std::string or std::vector could help you release the memory, in your case std::vector maybe a better choice, because it looks more like a buffer compare with std::string.

if(!file.is_open()){
  std::cerr<<"cannot open file\n";
  return -1;
}

auto const size = file.seekg(0, std::ios::end);
std::vector<char> buffer(size );
file.seekg(0, std::ios::beg);
file.read(&buffer[0], size); //same way to feed the data into std::string
file.close();

You could use std::unique_ptr too

auto buffer = std::make_unique<char[]> p(file.tellg());
file.read(buffer.get(), size); //same way to feed the data into std::string

However, I would prefer QFile to ease my pain rather than using std::ifstream

Also I'm not sure ifstream supports / in paths on Windows (Qt does). Try to replace / with \

/ works on my laptop(windows 10 64bits), using Qt5.7, visual c++ 2015 with update 3.

BadHombre

Thanks guys for the Help ! ... so the Problem is that getOpenFileNames gives me the Path like that :

("E:/test/file.bin")

to use it in if stream i need zu 2 Slashes after the Drive.. sth like :

("E://test/file.bin")

I tried to use :

QFile f("myfile");
Q
if (f.open(QIODevice::ReadOnly))
{

}

but it doesn't open the File ... Does sb know how i get a second slash after the without Hardcoding :/ Or why doesn 't qread work ?

jsulm

@BadHombre Why do you want to use ifstream? If you're already using Qt why not use QFile,...?

jsulm

@BadHombre said in Problem with ifstream and Qt Creator:

QFile f("myfile");

Did you check why it doesn't open the file? What is myfile? Absolute path? Relative path?
Did you check http://doc.qt.io/qt-5/qiodevice.html#errorString ?

BadHombre

@jsulm I tried now to use QFile ... and it seems to be working... but do you kno how i get the doubles of the file... For example read the doubles into a vector.. is this possible ?

Flotisable

@BadHombre
read QDataStream document

jsulm

@BadHombre Take a look at http://doc.qt.io/qt-5/qdatastream.html

BadHombre

Okay Thanks for your Help Guys :) I also found a way to realise it with ifstream for the people who maybe need it one day...

 QStringList filenames = QFileDialog::getOpenFileNames(
        this,
        tr("Choose "),
        "C://",
        "All files (*.*)");

    std::string current_locale_text = filenames[0].toLocal8Bit().constData();

    ifstream file(current_locale_text.c_str());