https://godbolt.org/

http://quick-bench.com/oWbDZZ1lqXq6G69k0PnPtZu2V40
#include <sstream>
#include <string>

static void StringCreation(benchmark::State& state) {
  // Code inside this loop is measured repeatedly
  for (auto _ : state) {
    std::stringstream s;
    std::string created_string("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque accumsan, felis sed finibus tincidunt, mauris sapien tempus neque, sit amet egestas ");
    for (int i=0 ; i<20000 ; i++)
    {
      s << created_string;

    }
    // Make sure the variable is not optimized away by compiler
    benchmark::DoNotOptimize(s);
  }
}
// Register the function as a benchmark
BENCHMARK(StringCreation);

static void StringCopy(benchmark::State& state) {
  // Code before the loop is not measured
  for (auto _ : state) {
    std::string s = "";
    std::string created_string("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque accumsan, felis sed finibus tincidunt, mauris sapien tempus neque, sit amet egestas ");
    for (int i=0 ; i<20000 ; i++)
    {
      s += created_string;

    }
    // Make sure the variable is not optimized away by compiler
    benchmark::DoNotOptimize(s);
  }
}
BENCHMARK(StringCopy);


https://regexcrossword.com/