QDomElement.setAttribute crashes program - c++

Question

It's confusing. My program was working reliably. Then, I did some changes in a hurry, they didn't work, re-winded them, went to show my program and it no longer works. My fault for not making new copy every 10min. The thing is however, the program crashes in a place which makes no sense.
QDomElement Expense::toNode()
{
QDomElement e=Entry::toNode(); //Entry is parent of Expense
QString temp;
//std::string getThis=e.nodeName().toStdString();
temp=QString::fromStdString(Category); //Category is string field
//e.hasAttribute("category"); //this works
//e.setAttribute("ha","hi"); //this crashes program
//e.setAttribute("category",temp); //this also crashes program
return e;
}
I thought that maybe in hurry I modified some library, but if I create a new QDomElement, and edit it's attributes, there is no problem at all. Then I thought that maybe my node is not a node at all, but I can use many other functions (like for example e.hasAttribute). Is there limit to amount of attributes we can set? What might be the error?
In case it helps:
QDomElement Entry::toNode()
{
QDomDocument d("EzXpns");
QDomElement e=d.createElement("entry");
QString temp;
temp=QString::fromStdString(Name);
e.setAttribute("name",temp);
temp=QString::fromStdString(to_string(static_cast<long double>(Amount)));
e.setAttribute("amount",temp);
temp=QString::fromStdString(to_string(static_cast<long long>(Date[0])));
e.setAttribute("dateyear",temp);
temp=QString::fromStdString(to_string(static_cast<long long>(Date[1])));
e.setAttribute("datemonth",temp);
temp=QString::fromStdString(to_string(static_cast<long long>(Date[2])));
e.setAttribute("dateday",temp);
temp=QString::fromStdString(Comment);
e.setAttribute("comment",temp);
return e;
}
Edit: I should have specified, that if I try to debug this is the message I get:
TestBuild.exe has triggered a breakpoint
then
Unhandled exception at 0x77d415de in TestBuild.exe: 0xC0000005: Access violation reading location 0x13fb8ff8.
then
0x77d3016e in TestBuild.exe: 0x00000000: The operation completed successfully.
Edit2: Sample xml
<!DOCTYPE data>
<EzXpns>
<account>
<login name="b" password="1"/>
<expHis>
<entry comment="9" dateday="1" name="k" dateyear="0" amount="9" datemonth="1"/>
<entry comment="9" dateday="1" name="b" dateyear="0" amount="9" datemonth="1"/>
<entry comment="9" dateday="1" name="b" dateyear="0" amount="9" datemonth="1"/>
<entry comment="9" dateday="1" name="b" dateyear="0" amount="9" datemonth="1"/>
<entry comment="9" dateday="1" name="b" dateyear="0" amount="9" datemonth="1"/>
</expHis>
<incomeHis/>
</account>
</EzXpns>

Answer 1

Solution was within the Qt documentation.
Look at how I create new element, I do it by calling QDomDocument d("EzXpns"); , which is a mistake. In Qt, after the QDomDocument is destroyed SO ARE ALL CHILD NODES. It worked before just because of pure luck. Creating one QDomDocument, and then passing it around, solved my problem.