CODEWITHSUNDEEP
c++qt
Seb
Seb

Reputation: 3215

Variable change without any direct action

I have wrote an API as defined below. This API is used to find the index of a filename in a file system. The filesystem is coming from an Android device through mtp. What I'm doing is to request a list of files stored on the Android device and compare each file listed to the one I'm looking for 'name2look'

I have created a vector table to store what I'm doing but it's not mandatory. My concerns is that the variable name2look contain the right name I'm looking for "Pictures"

uint32_t USBDevice::GetIndexFromName(LIBMTP_mtpdevice_t *dev, uint32_t storage,const char *name2look)
{
    uint32_t idx_fold = 1;
    std::vector<MyFileTreeItem*> FSimage;
    LIBMTP_file_t *files;
    LIBMTP_file_t *file;

    std::cout << "NAME : " << name2look << "\n";
    files = this->GetFileAndFolder(dev, storage,0);
    file = files;
    while (file != NULL) {
        MyFileTreeItem* FSitem = new MyFileTreeItem();
        FSitem->filename = file->filename;
        FSitem->index = file->item_id;
        FSitem->FileType = file->filetype;
        FSimage.push_back(FSitem);

        std::cout << "NAME : " << name2look << "\n";
        std::cout << "FS NAME : " << file->filename << "\n";
        if(std::strcmp(file->filename, name2look)==0) {
            std::cout << "FIND IDX : " << file->item_id << "\n";
            return file->item_id;
        }
        file = file->next;
    } 
    return 0;
}

The Log is showing that the first display 'std::cout' is ok. the variable name is still 'Pictures' but when I ask to display it after in the "while" the variable name2look change and is not the same anymore.

First display NAME : Pictures second one in the while NAME : Martin).mp3 FS NAME : Music

How is it possible to be corrupted ??

The function is called by a Qt C++ code:

void MyButtonGroup::buttonClick(QAbstractButton *button)
{
    uint32_t status;
    QList<QTreeWidgetItem *> itemList;
    uint32_t index = 0;

    if (button->text() == "Create Folder") {        
        itemList = this->MyTree->selectedItems();

        QString str = itemList[0]->text(0);
        char *utf8_text = str.toLatin1().data();
        if(utf8_text != NULL)
        {
            std::cout << "A CHERCHER " << utf8_text << "\n";
            index = this->MyDevice.GetIndexFromName(this->dev_id, storage->id, utf8_text);
        }
        else
            index = 0;

        CreateFolderDialog *dialog = new CreateFolderDialog(this->MyTree, this->MyDevice, this->dev_id, this->storage, index);
        dialog->show();
    }

utf8_text report the right value.

Any idea ?

Upvotes: 1

Views: 70

Answers (1)

Zan Lynx
Zan Lynx

Reputation: 54325

This might be the problem. I am not sure. Check it out.

This line:

char *utf8_text = str.toLatin1().data();

What does the documentation say toLatin1() does? It creates a new QByteArray object and then you call data() on that and you get a pointer to character and then the QByteArray is destroyed at the end of the line because it was TEMPORARY.

And now you have an invalid pointer to freed memory that you then pass into your function. It probably gets overwritten by the first call to new() in your function.

I think you should change it to something like this:

QByteArray latin_str = str.toLatin1();
char *utf8_text = latin_str.data();

Your name utf8_text is weird since you just converted it to Latin1 which isn't UTF8.

Upvotes: 1

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