writeCharacters() of QXmlStreamWriter crashed when writting the content of a big file to QBuffer - qt

Question

The following code use writeCharacters with small buffer size to writing the content of big file, but it seems it only works when writing the content to a xml file, but writeCharacters() will crash when writting the content of a big file to QBuffer, any solution? Thanks.
env: qt opensource 4.8.7; Visual Studio 2010; Windows 10;
big file: https://1drv.ms/u/s!Ap_EAuwC9QkXijbujBQcQk4Hat_O?e=KemgUY
#include <QtCore/QCoreApplication>
#include <QFile>
#include <QXmlStreamWriter>
#include <QBuffer>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QByteArray mContentBuffer;
QByteArray arr;
int pos, filesize;
QFile file("C:\\Work\\bigfile.xar"); //Szie: 300Mb
if(!file.open(QFile::ReadOnly))
{
return -1;
}
mContentBuffer = file.readAll();
file.close();
//QFile profile("C:\\Work\\profile.xml");
//if(!profile.open(QFile::WriteOnly|QFile::Truncate))
//{
// return -1;
//}
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QXmlStreamWriter stream(&buffer);
stream.setAutoFormatting(true);
stream.writeStartDocument();
stream.writeStartElement("Profile");
//stream.writeTextElement("Content", mContentBuffer.toBase64());
stream.writeStartElement("Content");
pos = 0;
filesize = mContentBuffer.size();
while(pos<filesize){
arr = mContentBuffer.mid(pos, 2000000);
stream.writeCharacters(arr.toBase64());
pos+=arr.size();
}
stream.writeEndElement();
stream.writeEndElement(); // Profile
stream.writeEndDocument();
return 0;
}
Here is the goal for writing a big file into a QBuffer.
bool profileModified()
{
bool result = true;
QFile profile("C:\\Work\\profile.xml");
if(profile.exists())
{
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QXmlStreamWriter stream(&buffer);
exportProfile(stream);
profile.open(QFile::ReadOnly);
QByteArray profileArr = profile.readAll();
buffer.seek(0);
QByteArray bufferArr = buffer.buffer();
result = (array_compare(profileArr, bufferArr) != 0);
profile.close();
}
return result;
}