Why does the std:: string operation perform poorly- Why do std::string operations perform poorly?

problem ：

I made a test to compare string operations in several languages for choosing a language for the server-side application. I did a test to compare string operations in several languages , To choose a language for the server-side application .The results seemed normal until I finally tried C++, which surprised me a lot. The result seems normal , Until I finally tried C++, This surprised me very much .So I wonder if I had missed any optimization and come here for help. So I want to know if I missed any optimizations and come here for help .

The test are mainly intensive string operations, including concatenate and searching. The tests are mainly intensive string operations , Including connection and search .The test is performed on Ubuntu 11.10 amd64, with GCC's version 4.6.1. Test in Ubuntu 11.10 amd64 On the implementation ,GCC Version is 4.6.1.The machine is Dell Optiplex 960, with 4G RAM, and Quad-core CPU. The machine is Dell Optiplex 960,4G Memory , Tetranuclear CPU.

in Python (2.7.2): stay Python (2.7.2) in ：

def test():    x = ""    limit = 102 * 1024    while len(x) < limit:        x += "X"        if x.find("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 0) > 0:            print("Oh my god, this is impossible!")    print("x's length is : %d" % len(x))test()

which gives result: This gives the result ：

x's length is : 104448real    0m8.799suser    0m8.769ssys     0m0.008s

in Java (OpenJDK-7): stay Java (OpenJDK-7) in ：

public class test {    public static void main(String[] args) {        int x = 0;        int limit = 102 * 1024;        String s="";        for (; s.length() < limit;) {            s += "X";            if (s.indexOf("ABCDEFGHIJKLMNOPQRSTUVWXYZ") > 0)            System.out.printf("Find!\n");        }        System.out.printf("x's length = %d\n", s.length());    }}

which gives result: This gives the result ：

x's length = 104448real    0m50.436suser    0m50.431ssys     0m0.488s

in Javascript (Nodejs 0.6.3) stay Javascript (Nodejs 0.6.3)

function test(){    var x = "";    var limit = 102 * 1024;    while (x.length < limit) {        x += "X";        if (x.indexOf("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 0) > 0)            console.log("OK");    }    console.log("x's length = " + x.length);}();

which gives result: This gives the result ：

x's length = 104448real    0m3.115suser    0m3.084ssys     0m0.048s

in C++ (g++ -Ofast) stay C++ (g++ -Ofast)

It's not surprising that Nodejs performas better than Python or Java.Nodejs Better performance than Python or Java It's not surprising .But I expected libstdc++ would give much better performance than Nodejs, whose result really suprised me. But I expect libstdc++ Will provide more than Nodejs Better performance , Its result really surprised me .

#include <iostream>#include <string>using namespace std;void test(){    int x = 0;    int limit = 102 * 1024;    string s("");    for (; s.size() < limit;) {        s += "X";        if (s.find("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 0) != string::npos)            cout << "Find!" << endl;    }    cout << "x's length = " << s.size() << endl;}int main(){    test();}

which gives result: This gives the result ：

x length = 104448real    0m5.905suser    0m5.900ssys     0m0.000s

Brief Summary Brief summary

OK, now let's see the summary: well , Now let's look at the summary ：

• javascript on Nodejs(V8): 3.1sNodejs（V8） Upper javascript：3.1s
• Python on CPython 2.7.2 : 8.8sCPython 2.7.2 Upper Python：8.8s
• C++ with libstdc++: 5.9s with libstdc++ Of C++：5.9 second
• Java on OpenJDK 7: 50.4sOpenJDK 7 Upper Java：50.4 second

Surprisingly! It's amazing ！I tried "-O2, -O3" in C++ but noting helped. I am here C++ I tried “-O2,-O3”, But it helps to notice .C++ seems about only 50% performance of javascript in V8, and even poor than CPython.C++ stay V8 There seems to be only javascript Of 50% performance , Even better than CPython Still bad .Could anyone explain to me if I had missed some optimization in GCC or is this just the case? Can someone explain to me if I missed GCC Some optimizations in , Or just this situation ？Thank you a lot. Thank you very much .

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Solution ：

Reference resources ： https://stackoom.com/en/question/Yrot