g++编译出的多线程程序出错“segmentation fault"

我使用的g++版本是g++ 4.4.3

升级到4.7版本：
add-apt-repository ppa:ubuntu-toolchain-r/test
apt-get update
apt-get install gcc-4.7-base
apt-get install gcc-4.7
apt-get install g++-4.7

update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.6 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.6
update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.7 40 --slave /usr/bin/g++ g++ /usr/bin/g++-4.7
update-alternatives --config gcc

重新编译：
g++ -std=c++0x A.cpp -o a
再次运行./a或者/tmp/a
再次错误：terminate called after throwing an instance of 'std::system_error'
  what():  Enable multithreading to use std::thread: Operation not permitted
Aborted
解决方法：
g++ -std=c++0x -pthread A.cpp -o a
再次运行./a或者/tmp/a
运行成功：
Launched from the main
Launched by thread 3
Launched by thread 4
Launched by thread 5
Launched by thread 6
Launched by thread 7
Launched by thread 8
Launched by thread 9
Launched by thread 2
Launched by thread 1
Launched by thread 0

代码例子：

#include <iostream>
#include <thread>
 
     static const int num_threads = 10;
 
     //This function will be called from a thread
 
     void call_from_thread(int tid) {
         std::cout << "Launched by thread " << tid << std::endl;
     }
 
     int main() {
        std::thread t[num_threads];
 
         //Launch a group of threads
         for (int i = 0; i < num_threads; ++i) {
             t[i] = std::thread(call_from_thread, i);
         }
 
         std::cout << "Launched from the main\n";
 
         //Join the threads with the main thread
         for (int i = 0; i < num_threads; ++i) {
             t[i].join();
         }
 
         return 0;
    }