How to load 500MB data from txt file in QT - qt

Question

I am working on a big (~500Mb) RAW txt file.
There are about 20,000,000 lines in the file.
Each line includes one double and one int. For example:
45782.1234852 10
Below is my simple code:
QTextStream rdStream(&qFile_Input);
while (!rdStream.atEnd())
{
//QStringList qList_data=rdStream.readLine().split(" ",QString::SkipEmptyParts);
rdStream.readLine();
}
It takes about 30 seconds just to read line QTextStream::readLine();
If I add .split(" ",QString::SkipEmptyParts) into a Qstringlist, then the total time required jumps to 5 minutes. My question is three fold:
Where does the time gap comes from?
Is there a way to get a shorter processing time?
If my file is larger than the RAM of PC, will I encounter an
error? If so, what can I do?
Thanks in advance!

Answer 1

Well, it seems that the splitting part adds an enormous overhead time-wise. Instead of using the Qt class QTextStream, you could probably just use the methods from the c++ standard library. You should get better performance than the 5 minutes you are seeing now.
#include <fstream>
int main()
{
std::ifstream infile("thefile.txt");
double a;
int b;
while(infile >> a >> b)
{
//Do something with a and b here, they've been read
}
return 0;
}