C++中头⽂件bitsstdc++.h的优缺点
C++ 中头⽂件<bits/stdc++.h>的优缺点⼀、总结
⼀句话总结：
> 1、bits/stdc++.h是部分C++中⽀持的⼀个⼏乎万能的头⽂件，包含所有的可⽤到的C++库函数，如<istream>/<ostream>/<stack>/<queue>等.
> 2、原理是在这个⽂件中包含了其它的头⽂件
// 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
gnu编译器// <Licenses - GNU Project - Free Software Foundation>.
/** @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
⼆、C++ 中头⽂件<bits/stdc++.h>的优缺点
在编程竞赛中，我们常见⼀个头⽂件：
#include <bits/stdc++.h>
发现它是部分C++中⽀持的⼀个⼏乎万能的头⽂件，包含所有的可⽤到的C++库函数，如<istream>/<ostream>/<stack>/<queue>.该头⽂件的详细内容如下：
1// C++ includes used for precompiling -*- C++ -*-
2
3// Copyright (C) 2003-2013 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23// <Licenses - GNU Project - Free Software Foundation>.
24
25/** @file stdc++.h
26 * This is an implementation file for a precompiled header.
27*/
28
29// 17.4.1.2 Headers
30
31// C
32 #ifndef _GLIBCXX_NO_ASSERT
33 #include <cassert>
34#endif
35 #include <cctype>
36 #include <cerrno>
37 #include <cfloat>
38 #include <ciso646>
39 #include <climits>
40 #include <clocale>
41 #include <cmath>
42 #include <csetjmp>
43 #include <csignal>
44 #include <cstdarg>
45 #include <cstddef>
46 #include <cstdio>
47 #include <cstdlib>
48 #include <cstring>
49 #include <ctime>
50
51#if __cplusplus >= 201103L
52 #include <ccomplex>
53 #include <cfenv>
54 #include <cinttypes>
55 #include <cstdalign>
56 #include <cstdbool>
57 #include <cstdint>
58 #include <ctgmath>
59 #include <cwchar>
60 #include <cwctype>
61#endif
62
63// C++
64 #include <algorithm>
65 #include <bitset>
66 #include <complex>
67 #include <deque>
68 #include <exception>
69 #include <fstream>
70 #include <functional>
71 #include <iomanip>
72 #include <ios>
73 #include <iosfwd>
74 #include <iostream>
75 #include <istream>
76 #include <iterator>
77 #include <limits>
78 #include <list>
79 #include <locale>
80 #include <map>
81 #include <memory>
82 #include <new>
83 #include <numeric>
84 #include <ostream>
85 #include <queue>
86 #include <set>
87 #include <sstream>
88 #include <stack>
89 #include <stdexcept>
90 #include <streambuf>
91 #include <string>
92 #include <typeinfo>
93 #include <utility>
94 #include <valarray>
95 #include <vector>
96
97#if __cplusplus >= 201103L
98 #include <array>
99 #include <atomic>
100 #include <chrono>
101 #include <condition_variable>
102 #include <forward_list>
103 #include <future>
104 #include <initializer_list>
105 #include <mutex>
106 #include <random>
107 #include <ratio>
108 #include <regex>
109 #include <scoped_allocator>
110 #include <system_error>
111 #include <thread>
112 #include <tuple>
113 #include <typeindex>
114 #include <type_traits>
115 #include <unordered_map>
116 #include <unordered_set>
117#endif
在编程竞赛中，使⽤这个头⽂件是⼀个好的想法，特别是当你在选择头⽂件时想减少时间，我们更加专注于到算法解决问题⽽不是软件⼯程。⽽从软件⼯程的视⾓，我们最好最⼩化包含头⽂件，如果你包含了⼀些你可能不会⽤到的头⽂件，就会增加不必要的编译时间和程序⼤⼩。
bits/stdc++的缺点
bits/stdc++.h 不是GNU C++库的标准头⽂件，所以如果你在⼀些编译器（除了GCC）上编译你的代码，可能会失败，⽐如MSVC没有这个头⽂件。
使⽤它会包含很多不必要的东西，并且会增加编译时间
这个头⽂件不是C++标准的⼀部分，所以是不可移植的，应该尽量避免。
尽管标准中有⼀些通⽤的头⽂件，但还是应该避免使⽤它来代替特定的头⽂件，因为编译器在每次编译转换单元时都实际地读取并解析每个包含的头⽂件(包括递归包含的头⽂件)。
bits/stdc++的优点
在⽐赛中，使⽤这个⽂件是⼀个好主意，当你想减少时间浪费在做选择的时候；特别是当你的排名对时间很敏感的时候。
这还减少了编写所有必要头⽂件的所有杂务。
你不必为使⽤的每个函数都记住GNU c++的所有STL。
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