Performance of C vs. C++

Monday, January 28. 2008

Performance of C vs. C++

David Tanzer recently blogged about comparing performance of equivalent C and C++ programs. He did so in order to be able to decide which of the two languages he should use as implementation language for his diploma thesis. In C, he used a classical dispatching mechanism, while in C++, he used inheritance and virtual methods. His result was that C++ was about 7 times slower with his test program. I couldn't believe this, and so I conducted my own tests, with a slightly modified source which can be downloaded here. I conducted tests of binaries with different optimization levels, all done with gcc/g++ 4.2.3 as provided by Debian unstable:

Optimization	C (average of 3 runs; [s])	C++ (average of 3 runs; [s])
-Os	38.778	34.001
-O3	27.951	32.722
-O2 -fomit-frame-pointer	27.985	31.562
-O0	33.271	34.192

Posted by Andreas Krennmair at 20:10 | Comments (3) | Trackbacks (0)

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How do reach so huge results? I get the following on my pc:

time: average of 3 runs; [s]

Optimization C C++
-Os 8.32233 5.43333
-O3 4.72300 5.42833
-O2 -fomit-frame-pointer 4.78267 5.15133
-O0 5.98233 5.74100

powered by gcc 4.2.3

#1 anonym on 2008-02-13 20:40 (Reply)

Erm, not every CPU has the same speed.

#1.1 ak (Homepage) on 2008-02-13 21:08 (Reply)

good test, but the "-Os"-part is not fair, look at the assembly....
The others are okay, C is in common a bit faster, but not much.

Another thing are the standard librarys, while C has only some simple functions,
C++ has a big standard library with implementations for vectors etc.
And the bad thing about that: Some of this implementations are not very efficient.
That's the biggest performence issue about C++ I would say.
I know, everyone can still use some more efficient librarys from somewhere in the internet or code his own implementation, but the average of C++ coders doesn't do that.

#2 kai on 2009-08-12 15:12 (Reply)

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