CODEWITHSUNDEEP
c++boostmacrosconst-iterator
ExiD
ExiD

Reputation: 87

Who is faster: BOOST_FOREACH macros or for

I tested my program and once decide to change BOOST_FOREACH macros to the simple for cycle with const_iterator.

and i receive unexpected result: program work slower with for.

Then i wrote small testing app:

std::vector<int> vec;
for (int i = 0; i != 50000000; ++i)
    vec.push_back(i);



time_t t1 = clock();
int sum1 = 0;
for (std::vector<int>::const_iterator it = vec.begin(); it != vec.end(); ++it)
    sum1 += *it;
std::cout << ulong(clock() - t1);

time_t t2 = clock();
int sum2 = 0;
BOOST_FOREACH(auto &it, vec) {
    sum2 += it;
}
std::cout << ulong(clock() - t2);

here is output:

34963
26964

Why so?

Upvotes: 0

Views: 72

Answers (1)

user3104201
user3104201

Reputation: 356

  1. You have undefined behaviour in your code. The sum of 0+...+50,000,000 is way beyond MAX_INT. Integer overflow == undefined behavior , undefined behavior== your tests are invalid.

  2. Assuming you built the project with full optimizations on, I'm guessing the results happen because of CPU warm-up and due the fact that In the second benchmark, some of the data is already cached. Try switching the benchmarkimg tests and see what happens

Upvotes: 5

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