std::string::operator+=() slow

• Key: STDCXX-492
• Type: Bug
• Status: Resolved
• Resolution: Fixed
• Priority: Major
• Assignee: Travis Vitek
• Reporter: Mark Brown
• Component/s: 21. Strings
• Affects Version/s: 4.1.3
• Fix Version/s: 4.2.0

Description

Comparing overloads of string::operator+=() in stdcxx with the same functions in gcc 4.1.2, stdcxx is up to twice slower than gcc:

$ time ./op_plus_equal-stdcxx 100000000 0

real 0m2.241s
user 0m1.932s
sys 0m0.204s
$ time ./op_plus_equal-stdcxx 100000000 1

real 0m2.540s
user 0m2.344s
sys 0m0.196s
$ time ./op_plus_equal-stdcxx 100000000 2

real 0m1.492s
user 0m1.308s
sys 0m0.184s
$ time ./op_plus_equal-gcc 100000000 0

real 0m0.883s
user 0m0.728s
sys 0m0.156s
$ time ./op_plus_equal-gcc 100000000 1

real 0m1.589s
user 0m1.424s
sys 0m0.168s
$ time ./op_plus_equal-gcc 100000000 2

real 0m1.131s
user 0m0.976s
sys 0m0.156s

#include <cassert>
#include <cstdlib>
#include <string>

int main (int argc, char *argv[])
{
const int N = argc < 2 ? 1 : std::atoi (argv [1]);
const int op = argc < 3 ? 0 : std::atoi (argv [2]);

std::string str;

const std::string x ("x");

if (op == 0) { for (int i = 0; i < N; ++i) str += 'x'; } else if (op == 1) { for (int i = 0; i < N; ++i) str += "x"; } else { for (int i = 0; i < N; ++i) str += x; }

assert (str.size () == std::size_t (N));
}