Problem with deleting QBuffer

[aiphae]

I have a FileHandler class to handle simple file operations (mainly .csv). I need it to be able to load files both from path (as QFile) and file data (as QBuffer). Here's the crucial part of the class:

#ifndef FILEHANDLER_H
#define FILEHANDLER_H

#include <QFile>
#include <QBuffer>
#include <QTextStream>
#include <QDir>

class FileHandler
{
public:
    FileHandler(const QString &path);
    FileHandler(const QByteArray &data, const QString &path = "");
    ~FileHandler();

private:
    QFile *file = nullptr;
    QBuffer *buffer = nullptr;
    QTextStream in; // For writing into a file
    QTextStream out; // For reading from a file
    QString path;
    bool useBuffer = false;
};

#endif // FILEHANDLER_H

FileHandler.cpp:

FileHandler::FileHandler(const QString &path)
    : path(path)
    , useBuffer(false)
{
    file = new QFile(path);
    out.setDevice(file);
    in.setDevice(file);
}

FileHandler::FileHandler(const QByteArray &data, const QString &path)
    : path(path)
    , useBuffer(true)
{
    buffer = new QBuffer();
    buffer->setData(data);
    out.setDevice(buffer);
    in.setDevice(buffer);
}

FileHandler::~FileHandler() {
    delete file;
    delete buffer;
}

In my widget I have the following code:

QString filename = QFileDialog::getOpenFileName(this, "Open File", QDir::homePath(), filter);
// Create a temporary handler to check if the file can be opened 
FileHandler *newHandler = nullptr;
if (filename.endsWith(".zip", Qt::CaseInsensitive)) {
    // Reading .csv from an archive
    // ...
    // ...
    newHandler = new FileHandler(file.readAll(), zipFilename);
}
else {
    // If .csv file was selected
    newHandler = new FileHandler(filename);
}

if (csvHandler) {
    csvHandler->close();
    csvHandler->clear();
}
delete csvHandler;

csvHandler = newHandler;

The problem arises only when I'm dealing with a FileHandler constructed with QByteArray, so when FileHandler has QBuffer initialized. The program crashes at the line delete csvHandler; with the "is_block_type_valid(header->_block_use)" OR "_crtisvalidheappointer(block)".

It DOES NOT happen when a FileHandler is constructed just with filepath. So as I understood, there is something wrong with deleteting QBuffer().

The archive processing works well and there is absolutely nothing wrong with it.

[Pl45m4]

@aiphae said in Problem with deleting QBuffer:

Is there a workaround?

I tried this on a release version and it's working well. But what if I want to debug it?

Simple: Link you release build to Qt release libs and your app's debug build to Qt's debug libs.

How did you install Qt?
You should have them.

[Christian Ehrlicher]

Where do you initialize file and buffer in the ctors? You currently only initialize them in one of the ctors.
Also I don't see a reason why QFile and QBuffer should be created with new instead using plain objects in the class.

[SGaist]

@Christian-Ehrlicher they are initialized at declaration time to nullptr.

That said, there's indeed no use for pointers here.

[aiphae]

@Christian-Ehrlicher said in Problem with deleting QBuffer:

Where do you initialize file and buffer in the ctors? You currently only initialize them in one of the ctors.
Also I don't see a reason why QFile and QBuffer should be created with new instead using plain objects in the class.

I want the class to handle EITHER QFile OR QBuffer. Because of this, I decided to make them pointers to save some memory.

UPD: I remade the code so it doesn't use pointers in the FileHandler class. It didn't help. Still the same error.

[Christian Ehrlicher]

@SGaist said in Problem with deleting QBuffer:

they are initialized at declaration time to nullptr.

Where do you see this?
Now there is also the header... hmm

[Christian Ehrlicher]

@aiphae said in Problem with deleting QBuffer:

. Still the same error.

Please provide some minimal, compilable code and a proper backtrace.

[aiphae]

@Christian-Ehrlicher said in Problem with deleting QBuffer:

@aiphae said in Problem with deleting QBuffer:

. Still the same error.

Please provide some minimal, compilable code and a proper backtrace.

Maybe this:

FileHandler *csvHandler = nullptr;
QVector<QString> files = {"path_1", "path_2"};

for (const auto &path: files) {
    FileHandler *newHandler = nullptr;
    newHandler = new FileHandler(QFile(path).readAll);
    delete csvHandler;
    csvHandler = newHandler;
}

FileHandler.h and FileHandler.cpp are above.

[Christian Ehrlicher]

This does not crash for me:

int main(int argc, char** argv)
{
    QApplication a(argc, argv);
    FileHandler* csvHandler = nullptr;
    QVector<QString> files = { "existing_file1.txt", "existing_file2.txt" };
    for (const auto& path : files) {
        QFile f(path);
        f.open(QIODevice::ReadOnly);
        auto newHandler = new FileHandler(f.readAll());
        delete csvHandler;
        csvHandler = newHandler;
    }
    delete csvHandler;
    return 0;
}

[aiphae]

@Christian-Ehrlicher

That's interesting. In my code I tried to replace newHandler = new FileHandler(file.readAll(), zipFilename); with newHandler = new FileHandler(file.readAll()); (without specifying a filename). No crash now. So the issue is not in QBuffer.

zipFilename is QString zipFilename = zip.getCurrentFileName();. I don't understand what's wrong...

[aiphae]

@Christian-Ehrlicher

Please try this:

int main(int argc, char** argv)
{
    QApplication a(argc, argv);
    FileHandler* csvHandler = nullptr;
    QVector<QString> files = { "existing_file1.txt", "existing_file2.txt" };
    for (const auto& path : files) {
        QFile f(path);
        f.open(QIODevice::ReadOnly);
        auto newHandler = new FileHandler(f.readAll(), path);
        delete csvHandler;
        csvHandler = newHandler;
    }
    delete csvHandler;
    return 0;
}

In this case the error should appear.

[Christian Ehrlicher]

No crash here and I also don't see a reason why it should crash.

[aiphae]

Well it crashes when I'm specifying path and it doesn't when I don't... It's weird.

[Christian Ehrlicher]

As I said before - please post the stacktrace.

[aiphae]

@Christian-Ehrlicher

This?

[Christian Ehrlicher]

You are most likely mixing debug and release libs - I would guess you link your debug app against Qt release libs. This is not supported on windows due to different msvc runtimes.

[aiphae]

@Christian-Ehrlicher said in Problem with deleting QBuffer:

You are most likely mixing debug and release libs - I would guess you link your debug app against Qt release libs. This is not supported on windows due to different msvc runtimes.

Is there a workaround?

I tried this on a release version and it's working well. But what if I want to debug it?

[Pl45m4]

@aiphae said in Problem with deleting QBuffer:

Is there a workaround?

I tried this on a release version and it's working well. But what if I want to debug it?

Simple: Link you release build to Qt release libs and your app's debug build to Qt's debug libs.

How did you install Qt?
You should have them.

[aiphae]

@Pl45m4 said in Problem with deleting QBuffer:

Simple: Link you release build to Qt release libs and your app's debug build to Qt's debug libs.

Yes. Apparently I was linking external release libraries instead of debug ones. The issue is solved. Thank you!