Re: String performance

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 20 Oct 2007 23:02:32 GMT

Message-ID:

<cOvSi.11818$ZA.7638@newsb.telia.net>

On 2007-10-20 23:26, Marcin Kalicinski wrote:

I have recently done a simple measurement of std::string performance in C++,
and I'm shocked how bad it is. C++ is first and foremost meant to be a
performance language, with near-zero overhead. This holds quite well with
regards to the language, but overheads of the std library are absolutely
abysmal. And string is one of the most often used datatypes.

The test program creates 10 million strings and puts them in a container
(see source code #1, #2 below).

// #2: C#
class Test
{
    public static void Main()
    {
        DateTime t1 = System.DateTime.Now;
        List<string> v = new List<string>();
        for (int i = 0; i < 10000000; ++i)
            v.Add("foo");
        DateTime t2 = System.DateTime.Now;
        Console.WriteLine(t2 - t1);
    }
}

I am not a C# expert, but I thing you are comparing apples and oranges
here. In C# a string is a reference type, and as you pointed out strings
are immutable. What your C# code above does is to create 1 (one) string
and then add 10000000 references to that in a container. The equivalent
C++ code would look something like this.

#include <time.h>
#include <iostream>
#include <vector>

int main()
{
    std::vector<char*> v;
    clock_t t1 = clock();
    for (int i = 0; i < 10000000; ++i)
        v.push_back("poo");
    clock_t t2 = clock();
    std::cout << double(t2 - t1) / CLOCKS_PER_SEC;
}

Runs in 0.2 sec in release mode, but my hardware is probably different
from yours.

As you can see there are two problems with this code, first of it does
not involve strings and second, it only measures the performance of your
vector implementation.

--
Erik Wikstr??m