Test for reversing a string

test.cpp

#include <ctime>
#include <iostream>


void r2(std::string& source)
{
    // Step 1: reverse the string.
    std::reverse(std::begin(source), std::end(source));

    // Step 2: Reverse each word in the string.
    //         This puts them back the correct way around
    auto const end = std::end(source);      // The very end
    auto       back= std::begin(source);    // One past the end of the last word
    auto       next= back;                  // The start of the next word

    // Loop over the string finding words.
    for(auto item = next; back != end; item = next) {
        back = std::find(item, end, '.');
        std::reverse(item, back);           // Reverse a found word.
        next = back + 1;
    }
}
  
void r1(std::string& source)
{
    std::string result;
    size_t source_length = source.size();
    size_t end = source_length;

    // Loop from end of string to reverse the domains
    for (int i = source_length; i >= 0; i--) {

        // If not domain divider, continue
        if (source[i] != '.') {
            continue;
        }

        // Append the domain substring
        result.append(source, i+1, end - i);
        result += '.'; // Append divider
        end = i-1; // Set end point of next domain
    }
    // Copy the last bit of source string, if needed
    if ((end = result.size()) != source_length) {
        result.append(source, 0, source_length - end);
    }
    source = std::move(result);
}


int main()
{
    std::string     test    = "this.is.a.subdomain";
    std::cout << std::time(nullptr) << "\n";
    for(int loop=0;loop < 100'000'000; ++loop) {
        r1(test);
    }
    std::cout << std::time(nullptr) << "\n";
    for(int loop=0;loop < 100'000'000; ++loop) {
        r2(test);
    }
    std::cout << std::time(nullptr) << "\n";
}

> g++ -O3 -std=c++1z pl.cpp
> ./a.out
1449457676
1449457686
1449457689