With or Without Qt
August 24, 2009 by André | Comments
I wanted to do a certain bit of benchmarking for quite a while - years actually - but triggered by one of those friendly discussions on the ##c++ channel on FreeNode I finally figured I should sit down and actually do it. I was expecting some interesting results, but the not at the scale that we will see below.
If you ask the resident channel bot on ##c++ how to tokenize a std::string you'll get offered the following (slightly compacted) code snippet:
#include <sstream>
#include <vector>
#include <string>std::string str("abc:def");
std::istringstream split(str);
std::vector<std ::string> tokens;
for (std::string each; std::getline(split, each, ':'); tokens.push_back(each));
Obviously, that's the "Without Qt" version: Clean Standard C++, as straight-forward as it can get. The contender "With Qt" is:
#include <QString>
#include <QStringList>QString str("abc:def");
QStringList tokens = str.split(':');
From the source alone we can collect a few numbers:
Property | Without Qt | With Qt | Ratio |
Code to type | 3 lines | 1 line | 3.0 |
147 char | 35 chars | 4.2 | |
Code usable as sub-expression | no | yes | |
Size of compilation unit [1] | 22215 lines | 7590 lines | 2.9 |
Compile time [2] | 1.64s | 1.02s | 1.6 |
To compare performance I use a benchmark that I just checked into the Qt source base, under tests/benchmark/qstringlist. It basically consists of running the above mentioned snippets on a string "unit:unit:unit:...." with 10, 100, 1000, and 10000 "unit" chunks and record callgrind's "instruction loads per iteration" as follows:
Chunk count | Without Qt | With Qt | Ratio |
10 chunks | 18,455 | 9,827 | 1.9 |
100 chunks | 134,578 | 71,008 | 1.9 |
1000 chunks | 1,244,425 | 641,174 | 1.9 |
10000 chunks | 13,161,115 | 7,053,633 | 1.9 |
In this case, bigger numbers mean more time needed to execute. Interesting, isn't it?
After reading Thiago's latest posts I got the impression that people like conclusions. The verbose version of a conclusion might be something along the lines of
Using Qt's functions to split a string you need about a third of the effort to write code, and get a 47% performance boost at runtime.
Or shorter (Qt way): "Code less, create more".
André
[1] Counted with "g++ -E -DQT_NO_STL -I$QTDIR/include/QtCore -I$QTDIR/include qt.cpp | wc" using g++ Ubuntu 4.3.3-5ubuntu4.
[2] Fastest result of "real" time, out of 20 runs each. "user" times in both scenarios smaller, with similar ratio.
Blog Topics:
Comments
Subscribe to our newsletter
Subscribe Newsletter
Try Qt 6.5 Now!
Download the latest release here: www.qt.io/download.
Qt 6.5 is the latest Long-Term-Support release with all you need for C++ cross-platform app development.
Explore Qt World
Check our Qt demos and case studies in the virtual Qt World
We're Hiring
Check out all our open positions here and follow us on Instagram to see what it's like to be #QtPeople.
Näytä tämä julkaisu Instagramissa.Henkilön Qt (@theqtcompany) jakama julkaisu