最近發現了一個C++的頭文件bits/stdc++.h，聽說這是一個幾乎包含了所有C++庫函數的頭文件，就想更深入的了解一下，下面是頭文件內容
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
看了別人對於這個頭文件的看法，自己也有了更深的認識，包含大量不需要的庫的頭文件，更適合在oj比賽中使用。如果在軟件工程的開發中，我們應該減少包含，控制編譯時間和代碼大小。
優點如下：
1.在競賽中節約時間
2.減少了編寫所有必要頭文件的工作量
3.對於使用的每個函數，不用記住GNU C++的所有STL
缺點如下：
1.不屬於GNU C++庫的標准頭文件，在部分情況下可能會失敗
2.使用它將包含許多不必要的東西，並增加編譯時間
3.這個頭文件不是C++標准的一部分，因此是不可移植的，應該避免
4.編譯器每次編譯翻譯單元時都必須實際讀取和分析每個包含的頭文件，應該減少這類頭文件的使用
參考地址：
https://blog.csdn.net/qq_20240999/article/details/59111606