Hmm I happen to use the idea of replacing begin with rbegin and iterators with reverse_iterator, etc Doing this I wrote a simple test file to compare performance. To my surprise doing std::reverse(v.begin(), v.end()) and than using BOOST_FOREACH is actually faster than a hard brute force method of BOOST_FOREACH_REV.
Test ran with mingw compiler 3.4.5
Heres the code.
#include <vector>
#include <iostream>
#include <algorithm>
#include <boost/timer.hpp>
#include <boost/foreach.hpp>
#include <boost/format.hpp>
int main()
{
const long TOTAL_ELEMENT = 10000;
std::cout << boost::format("%f\t%f\n") % "BOOST_FOREACH" % "BOOST_FOREACH_REV";
boost::timer t;
std::vector<int> vec_int;
for (int j = 1; j < 50; ++j)
{
vec_int.reserve(TOTAL_ELEMENT*j);
double t1, t2;
for (int i = 0; i < TOTAL_ELEMENT*j; ++i)
{
vec_int.push_back(i);
}
t.restart();
std::reverse(vec_int.begin(), vec_int.end());
BOOST_FOREACH(int& i, vec_int)
{
i -= 1;
}
t1 = t.elapsed();
t.restart();
BOOST_FOREACH_REV(int& i, vec_int)
{
i -= 1;
}
t2 = t.elapsed();
std::cout << boost::format("%f\t%f\n") % t1 % t2;
}
}
/*
BOOST_FOREACH BOOST_FOREACH_REV
0.001000 0.001000
0.002000 0.003000
0.002000 0.005000
0.004000 0.005000
0.005000 0.006000
0.003000 0.009000
0.010000
0.008000
0.008000 0.010000
0.008000 0.010000
0.008000 0.014000
0.009000 0.016000
0.016000 0.014000
0.010000 0.019000
0.011000 0.017000
0.013000 0.017000
0.013000 0.018000
0.014000 0.022000
0.016000 0.020000
0.016000 0.021000
0.017000 0.023000
0.017000 0.025000
0.018000 0.031000
0.018000 0.026000
0.020000 0.034000
0.019000 0.030000
0.022000
0.037000
0.021000 0.033000
0.024000 0.032000
0.023000 0.039000
0.025000 0.033000
0.026000 0.039000
0.026000 0.046000
0.029000 0.040000
0.028000 0.039000
0.030000 0.042000
0.030000 0.051000
0.032000 0.051000
0.035000 0.059000
0.035000 0.054000
0.033000 0.055000
0.035000 0.059000
0.035000 0.119000
0.035000 0.062000
0.037000 0.059000
0.037000
0.057000
0.037000 0.063000
0.072000 0.061000
0.039000 0.062000
0.039000 0.060000
*/
On 8/6/07, chun ping wang <
cablepuff@gmail.com> wrote:HI, yeah i wanted to do reverse iteration lookup so I took liberty to edit the file of
foreach.hpp. Its ugly but it "works". I haven't done any detail testing.
I only test it on basic string.. so i am sure of that.