A howl on the wind…

A performance benchmark of which include guard method is faster. Test times the compilation of a main.cpp that includes 10000 files 3 times each.

The tested methods are:

• #pragma once followed by #ifndef
• #ifndef followed by #pragma once
• Only #pragma once
• Only #ifndef
• External #ifndef

Sources for the test is at inc.tar.gz, but it’s just 5×10000 files.

The compilers are Microsoft Visual C++ 2010, GNU g++ 4.6.1, and LLVM clang++ 2.9.

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(There is also a string-to-int performance test.)

A performance benchmark of which method is faster of converting an std::string to a double. The goal is ending up with a double of the value represented in an std::string.

The tested methods are:

• a hand-written naive loop
• atof()
• strtod()
• sscanf()
• boost::lexical_cast<double>()
• boost::spirit::qi::parse()
• std::stringstream
• std::stringstream, reusing the object

Source for the test is at speed-string-to-double.cpp with cycle.h.

The compilers are Microsoft Visual C++ 2010 with _SECURE_SCL disabled, GNU g++ 4.6.0, and LLVM clang++ from Arch.

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A performance comparison of the speed of various ways to compare strings in C++. In this test, all comparisons are of not-equal strings.

Idea from #C++ on QuakeNet, where we always advocate using std::string over various char* functions. I wondered what, if any, the penalty for doing so was.

Sources

• Ticks counted via cycle.h (local mirror)
• Source: speed-string-compare.cpp

Things Tested

• a hand-written naive comparator loop; used as baseline
• string == string
• string == const char*
• strcmp(const char*, const char*) == 0
• strcmp(const char*, string.c_str()) == 0
• strcmp(string.c_str(), string.c_str()) == 0
• string.compare(string)
• string.compare(const char*)
• …and then the whole thing with different offsets.

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A performance comparison of the speed of various ways to read an entire file into an std::string in C++.

Idea from BD-Calvin in #C++ on QuakeNet.

Sources

• Ticks counted via cycle.h (local mirror)
• Source: speed-read-whole-file.cpp
• File used was generated with dd if=/dev/urandom of=random100 bs=1M count=100

Things Tested

• writing to a stringstream, then pulling data out as string
• constructing a string via streambuf_iterator
• getting file size via seeking, then preallocating a string to read into
• getting file size via stat(), then ditto…

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(Updated 2010-10-27: Re-run the test with latest clang++ from subversion)

A performance comparison of the speed of dynamic_cast operations in C++.

Idea from http://www.nerdblog.com/2006/12/how-slow-is-dynamiccast.html, who did not provide any source so I wrote my own more extensive tests.

Sources

• Ticks counted via cycle.h (local mirror)
• Source: speed-dynamic-cast.cpp

Things Tested

• reinterpret_cast on a known type
• virtual function call + reinterpret_cast
• member variable access + reinterpret_cast
• successful dynamic_cast to its own type
• successful dynamic_cast from the derived levels to lower levels
• failed dynamic_cast from the derived levels to an unrelated type

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