#include<bits/stdc++.h>包含了目前c++所包含的所有头文件
对比：
#include <iostream>
#include <cstdio>
#include <fstream>
#include <algorithm>
#include <cmath>
#include <deque>
#include <vector>
#include <queue>
#include <string>
#include <cstring>
#include <map>
#include <stack>
#include <set> using namespace std;
int main(){
return 0;
}
可以直接转化为：
#include<bits/stdc++.h>
using namespace std;
int main()
return 0;
}
兼容性问题：
注意，目前POJ还不支持<bits/stdc++.h>（G++、C++都不支持）。HDU部分支持（G++支持，C++不支持）。
其他国外的oj，还有*的oj都支持，CF，Topcoder也都支持。
当然，其实这是一个偷懒的写法，但是会降低编译速度（为何会降低编译速度，我还不能知道，等到之后学编译原理再来填坑吧）。
笔试平台可以使用，方便，VS中并不支持,一般G++ 4.4以上就支持这个头文件了。当然，私下自己学习就不要去使用了，对你的自主学习一点都没有好处。
c++11支持这个
po上<bits/stdc++.h>的源代码
// C++ includes used for precompiling -*- C++ -*-
// Copyright (C) 2003-2014 Free Software Foundation, Inc.//// This file is part of the GNU ISO C++ Library. This library is free// software; you can redistribute it and/or modify it under the// terms of the GNU General Public License as published by the// Free Software Foundation; either version 3, or (at your option)// any later version.
// This library is distributed in the hope that it will be useful,// but WITHOUT ANY WARRANTY; without even the implied warranty of// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional// permissions described in the GCC Runtime Library Exception, version// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and// a copy of the GCC Runtime Library Exception along with this program;// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see// <http://www.gnu.org/licenses/>.
/** @file stdc++.h
* This is an implementation file for a precompiled header.
*/
// 17.4.1.2 Headers
// C#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdalign>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>#endif
// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>#endif