Monthly ArchiveFebruary 2012
C++ 25 Feb 2012 13:19:21
C++ vector vs realloc()
A comparison of how many reallocations a worse case poorly coded use of realloc() does, compared to just using std::vector. 10000000 integers are added to the containers one-by-one. Clearly you would never abuse realloc() like this in real code, but it’s interesting nonetheless. Idea from sacrebleu at Freenode’s ##C++.
The full source is available in svn as a CMake project for easy cross-platform testing. Primary source vector-realloc.cpp
| Allocs / OS | std::vector | realloc() |
|---|---|---|
| Windows 7 | 40 | 9526 |
| Linux: Arch | 24 | 367 |
| Linux: Fedora 10 | 24 | 438 |
| Mac OS X | 24 | 31 |
- Mac OS X: OS X 10.7.3, 2.3 GHz Core i5, 8 GiB RAM. XCode 4.3, clang++ 3.1 -std=c++0x -stdlib=libc++ -O3.
- Windows 7: 64 bit, 1.60GHz Core i7 Q720, 8 GiB RAM. MSVC++ 2010 _SECURE_SCL=0
- Linux: Arch: VirtualBox on the Windows machine, VT-x, Arch Linux, kernel 3.2.7-1-ARCH x86_64, 1 GiB RAM. GNU g++ 4.6.2 -std=c++0x -O3
- Linux: Fedora 10: Fedora 10, kernel 2.6.27 x86_64, 2.66GHz Xeon, 8 GiB RAM. GNU g++ 4.4.1 -O3
C++ 20 Feb 2012 16:12:15
C++ Set Performance 2
(Old version from 2010-04-02)
A performance comparison of the speed of operations on the various set implementations used in C++. There are 16383 unique elements across which 1000000 insert, lookup, iterate, and erase operations are performed.
The raw tick numbers are shown and table sorting is enabled so you can compare for yourself. Just be aware that the Mac OS X, Linux, and Windows numbers cannot be compared against each other.
The full source is available in svn as a CMake project for easy cross-platform testing.
Sources
- Containers:
- std::set, std::unordered_set, boost::unordered_set – the usual general purpose suspects.
- CG3::sorted_vector, std::vector based replacement for std::set. Suitable for small amounts of cheap objects, such as integers.
- CG3::sorted_deque, rubbish version of sorted_vector.
- CG3::interval_vector, specialized for storing integers that form intervals.
- sti::sset, skip-list based std::set replacement. Wouldn’t compile with g++ or clang++.
- Ticks counted via cycle.h (local mirror)
- Source: CMake Project: benchmarks, primary source set.cpp
