Re: Generally, are the programs written by C++ slower than written by C 10% ?

From:
Paavo Helde <myfirstname@osa.pri.ee>
Newsgroups:
comp.lang.c++
Date:
Tue, 06 Sep 2011 11:47:55 -0500
Message-ID:
<Xns9F58C9669BC01myfirstnameosapriee@216.196.109.131>
KaiWen <wenkai1987@gmail.com> wrote in
news:c7c6ebac-3a50-443e-a864-55f25df6ed54@g32g2000pri.googlegroups.com:

#include <iostream>
#include <string>
#include <cstring>


#include <clock.h>

int main() {
        clock_t tbeg;

        {
                tbeg = clock();
                for (int i = 0; i < 10000000; i++)
                        std::string("hello, world!");

                std::cout << "test 1 use " << clock() - tbeg <<
std::endl;
        }

        {
                tbeg = clock();
                for (int i = 0; i < 10000000; i++) {
                        char* str = new char[20];
                        strcpy(str, "hello, world!");
                        delete [] str;
                }

                std::cout << "test 2 use " << clock() - tbeg <<
std::endl;
        }

        {
                tbeg = clock();
                for (int i = 0; i < 10000000; i++) {
                        char* str = (char*)malloc(20);
                        strcpy(str, "hello, world!");
                        free(str);
                }

                std::cout << "test 3 use " << clock() - tbeg <<
std::endl;
        }

        {
                tbeg = clock();
                for (int i = 0; i < 10000000; i++) {
                        char str[20];
                        strcpy(str, "hello, world!");
                }

                std::cout << "test 4 use " << clock() - tbeg <<
std::endl;
        }

        return 0;
}

output:
----------------------------
test 1 use 1260000
test 2 use 850000
test 3 use 610000
test 4 use 20000


My results (MSVC2010, Release x64 build):

test 1 use 160
test 2 use 476
test 3 use 417
test 4 use 0

The absolute values are not interesting as the clock() tick length is
platform-specific. However, std::string is much faster here than
malloc/new. I guess the small string optimization kicked in so
std::string did not perform any dynamic memory allocation at all.

Test 4 probably got optimized away completely.

cheers
Paavo

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