[Bug libstdc++/59116] New: std::nth_element segfaults by invalidating one of the vector elements

[chandraprakashblr at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59116

            Bug ID: 59116
           Summary: std::nth_element segfaults by invalidating one of the
                    vector elements
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chandraprakashblr at gmail dot com

std::nth_element segfaults by invalidating one of the vector elements.

Note : Replacing nth_element by partial_sort works fine.

Trying nth_element less than 6 also doesn't result in segfault.


Sample program : 

#include <iostream>
#include <vector>
#include <algorithm>
#include <cassert>

int main()
{
  for (size_t i(0); i < 1000; ++i) {
    std::vector<int> vec;
    uint32_t nth_element = 7;

    for (size_t i(0); i < 10; ++i) {
      vec.push_back(std::rand());
      std::cout << " n = " << vec.back() << std::endl;
    }
    assert((vec.size() >= nth_element));
    std::nth_element(vec.begin(), vec.begin() + nth_element, vec.end());
  }    
}


// commandline:  g++ nth_element.cc -std=c++11  -Wall -Wextra 



// stack trace

Program received signal SIGSEGV, Segmentation fault.
0x0000000000401fdf in __gnu_cxx::__normal_iterator<int*, std::vector<int,
std::allocator<int> > >
std::__unguarded_partition<__gnu_cxx::__normal_iterator<int*, std::vector<int,
std::allocator<int> > >, int>(__gnu_cxx::__normal_iterator<int*,
std::vector<int, std::allocator<int> > >, __gnu_cxx::__normal_iterator<int*,
std::vector<int, std::allocator<int> > >, int const&) ()


// system info

OS Ubuntu 13.10 (64 bit)

gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.8.1-10ubuntu8' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.8 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin
--with-system-zlib --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu8)