Why do std::string operations perform poorly?

Question

I made a test to compare string operations in several languages for choosing a language for the server-side application. The results seemed normal until I finally tried C++,

Answer 1

As mentioned by sbi, the test case is dominated by the search operation. I was curious how fast the text allocation compares between C++ and Javascript.

System: Raspberry Pi 2, g++ 4.6.3, node v0.12.0, g++ -std=c++0x -O2 perf.cpp

C++ : 770ms

C++ without reserve: 1196ms

Javascript: 2310ms

C++

#include 
#include 
#include 
using namespace std;
using namespace std::chrono;

void test()
{
    high_resolution_clock::time_point t1 = high_resolution_clock::now();
    int x = 0;
    int limit = 1024 * 1024 * 100;
    string s("");
    s.reserve(1024 * 1024 * 101);
    for(int i=0; s.size()< limit; i++){
        s += "SUPER NICE TEST TEXT";
    }

    high_resolution_clock::time_point t2 = high_resolution_clock::now();
    auto duration = std::chrono::duration_cast( t2 - t1 ).count();
    cout << duration << endl;
}

int main()
{
    test();
}

JavaScript

function test()
{
    var time = process.hrtime();
    var x = "";
    var limit = 1024 * 1024 * 100;
    for(var i=0; x.length < limit; i++){
        x += "SUPER NICE TEST TEXT";
    }

    var diff = process.hrtime(time);
    console.log('benchmark took %d ms', diff[0] * 1e3 + diff[1] / 1e6 );
}

test();