c++万能开头<bits/stdc++.h>

简单介绍下C++的万能头文件

一.开头

当年你还不知道C++万能头代码的时候:

#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
using namespace std;
int main(){  
    
    return 0;
}

当你知道了以后:

#include
using namespace std;
int main(){

    return 0;
}

#include几乎包含了目前c++中所包含的所有头文件 

二.源码

c++&c语言:

// C++ includes used for precompiling -*- C++ -*-
 
// Copyright (C) 2003-2013 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
// .
 
// 17.4.1.2 Headers
 
// C
#ifndef _GLIBCXX_NO_ASSERT
#include 
#endif
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
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#include 
#include 
#include 
 
#if __cplusplus >= 201103L
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#endif
 
// C++
#include 
#include 
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#if __cplusplus >= 201103L
#include 
#include 
#include 
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#include 
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#include 
#include 
#include 
#include 
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#include 
#endif

三.使用(dev c++)

#include//写到此处即可 
using namespace std;
int main(){

	return 0;
}

四.优缺点

优点如下:

    1.在竞赛中节约时间

    2.减少了编写所有必要头文件的工作量

    3.对于使用的每个函数,不用记住GNU C++的所有STL

缺点如下:

    1.不属于GNU C++库的标准头文件,在部分情况下可能会失败

    2.使用它将包含许多不必要的东西,并增加编译时间

    3.这个头文件不是C++标准的一部分,因此是不可移植的,应该避免

    4.编译器每次编译翻译单元时都必须实际读取和分析每个包含的头文件,应该减少这类头                   文件的使用

参考地址:https://www.cnblogs.com/blogxjc/p/11130843.html(仅为参考)

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