この記事は ICPC OB/OG の会(JAG)による 2021年度模擬地区予選問題の一部ネタバレが含まれます。
「ICPC？ なにそれ」な人は気にせずにお読み下さい。
これから2021年度JAG模擬地区を解こうと考えている方は、解法自体には触れませんが、お気をつけ下さい。
† #include<bits/stdc++.h> †
皆さんはC/C++のソースコードを読んでいて、 #include<bits/stdc++.h> と書かれたソースコードに出会ったことはあるでしょうか？
これはコンパイラにGCCを使用していると使える、すべての標準ライブラリを一度にインクルードできるヘッダファイルです。
主に競技プログラミング界隈、特にICPCや情報オリンピック本選など、ソースコードの準備が許されず、コンテスト時間内に全ての解答を1から書かないといけない場所で重宝されます。詳しい説明は以下の記事を参照して下さい。
この様に特定の用途では便利ですが、GCC を使っていないと使えない、非標準機能 なので、例えば Visual Studio や clang では使用できません。Mac の gcc も、デフォルトのものは中身は clang なので使用できません。
普段は gcc を使用しているけど、提出してみると何かがおかしい・clang の方が高速に実行されるかもとなり clang で提出することもあるかもしれません。そのとき、bits/stdc++.h を使っていると無慈悲に CE と言われてしまいます。
#if __has_include(<bits/stdc++.h>)
#include <bits/stdc++.h>
#endif // bits/stdc++
と書けば <bits/stdc++.h> がある場合のみ include されることになりclang でも安心ですが、やはり include 漏れしたときにどのヘッダをincludeしないといけないか調べる時間ロスが発生してしまいます。
include の仕組み
C/C++ のincludeは、基本的に他のファイルをそこに展開するだけであるので、例えばヘッダAがヘッダBをincludeしているとき、ヘッダAをincludeさえすればヘッダBもincludeされます。
例えば <map> を include すれば、std::map ではstd::pair も使用されているため、<utility>ヘッダもincludeされることが多いです。
※ この例では std::pair が使えればいいだけで、言語仕様的には <utility>ヘッダを include されるとは明示されているわけではありません。例えば <internal/pair_impl> に実装が書かれていて、そちらが include される可能性はあります。言語仕様で示されている例であれば、<utility> は <initializer_list> を include される、などがあります。
というわけで非標準である bits/stdc++.h を避けつつ、標準ライブラリヘッダを全て include するために、最小で何個の標準ライブラリヘッダのincludeが必要かという話をします。
bits/stdc++.h の中身を確認する
GCC が手元にあれば bits/stdc++.h を探して直接見てみても良いですし、ネット上 でも確認することができます。
GCC や clang を使っている場合、コンパイルオプションに -H を追加すると include しているヘッダが全て表示されるので、#include<bits/stdc++.h> が含まれるコードを -H 付きでコンパイルすることでも場所を確認できます。
GCC9.3.0 を入れた Ubuntu では /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h にありました。
GCCのバージョンや、C か C++か、また言語バージョンにもよって何が include されるかは微妙に変わりますが、GCC9.3.0 の C++17 では以下の88ヘッダが include されるようです。
cassert, cctype, cerrno, cfloat, ciso646, climits, clocale, cmath, csetjmp, csignal, cstdarg, cstddef, cstdio, cstdlib, cstring, ctime, cwchar, cwctype, ccomplex, cfenv, cinttypes, cstdalign, cstdbool, cstdint, ctgmath, cuchar, algorithm, bitset, complex, deque, exception, fstream, functional, iomanip, ios, iosfwd, iostream, istream, iterator, limits, list, locale, map, memory, new, numeric, ostream, queue, set, sstream, stack, stdexcept, streambuf, string, typeinfo, utility, valarray, vector, array, atomic, chrono, codecvt, condition_variable, forward_list, future, initializer_list, mutex, random, ratio, regex, scoped_allocator, system_error, thread, tuple, typeindex, type_traits, unordered_map, unordered_set, shared_mutex, any, charconv, filesystem, optional, memory_resource, string_view, variant, bit, version
cstdio 等のように c から始まる C言語時代からのヘッダも含まれますが、とりあえずこれらをこの記事では標準ライブラリヘッダと呼ぶことにします。
それぞれが何を include するか確かめる
これらの標準ライブラリヘッダが、中身で何を include するか確かめます。今回はこれらを1つずつincludeするソースコードを生成して、-H で実際にincludeされるヘッダを確認します。
C++の仕様書で、～は～を include すると明示的に記述されているものもあり、そちらを基準にするべきかもしれませんが、明示されてない include 関係も多くあるので、今回の方式にしました。
Clang 10.0.0 の C++17 では、この様になりました（長いので折りたたみ）
cctype 0
chrono 8
climits cstddef cstdint ctime limits ratio type_traits version
ctime 0
vector 22
algorithm atomic bit climits cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
iomanip 41
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new ostream ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
cstdint 0
future 35
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory mutex new ratio stdexcept string string_view system_error thread tuple type_traits typeinfo utility version
locale 37
algorithm atomic bit cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd iterator limits memory mutex new ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
string 26
algorithm atomic bit cctype cstddef cstdint cstdio cstdlib cstring cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new stdexcept string_view tuple type_traits typeinfo utility version
random 44
algorithm atomic bit bitset cctype cerrno chrono climits cmath cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new numeric ostream ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility vector version
condition_variable 33
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
cstddef 2
type_traits version
memory 17
atomic cstddef cstdint cstdlib cstring exception initializer_list iosfwd iterator limits new stdexcept tuple type_traits typeinfo utility version
functional 18
atomic cstddef cstdint cstdlib cstring exception initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
cwctype 1
cctype
streambuf 35
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd iterator limits memory mutex new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
cstring 0
cassert 0
numeric 20
atomic cmath cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
typeindex 13
cstddef cstdint cstdlib cstring exception initializer_list iosfwd limits new type_traits typeinfo utility version
cmath 4
cstddef limits type_traits version
unordered_map 23
algorithm atomic bit cmath cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new optional stdexcept tuple type_traits typeinfo utility version
stack 22
algorithm atomic bit cstddef cstdint cstdlib cstring deque exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
cfloat 0
bit 5
cstddef iosfwd limits type_traits version
array 21
algorithm atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
utility 7
cstddef cstdint cstring initializer_list iosfwd type_traits version
scoped_allocator 18
atomic cstddef cstdint cstdlib cstring exception initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
type_traits 2
cstddef version
atomic 4
cstddef cstdint type_traits version
codecvt 34
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory mutex new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
version 0
forward_list 21
algorithm atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
thread 33
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
csetjmp 0
ctgmath 45
algorithm atomic bit bitset ccomplex cctype cerrno chrono climits cmath complex cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new ostream ratio sstream stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
stdexcept 7
cstddef cstdlib exception iosfwd limits type_traits version
cstdio 0
set 22
algorithm atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new optional stdexcept tuple type_traits typeinfo utility version
mutex 33
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
iostream 41
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new ostream ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
filesystem 44
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype deque exception functional initializer_list iomanip ios iosfwd istream iterator limits locale memory mutex new ostream ratio stack stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
charconv 6
cerrno cstddef iosfwd limits type_traits version
exception 5
cstddef cstdlib limits type_traits version
unordered_set 23
algorithm atomic bit cmath cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new optional stdexcept tuple type_traits typeinfo utility version
new 6
cstddef cstdlib exception limits type_traits version
ostream 39
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd iterator limits locale memory mutex new ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
variant 22
algorithm array atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
climits 0
cstdlib 4
cstddef limits type_traits version
cstdarg 0
iosfwd 0
cwchar 2
cctype cwctype
cerrno 0
cinttypes 1
cstdint
deque 21
algorithm atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
sstream 41
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new ostream ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
initializer_list 3
cstddef type_traits version
bitset 28
algorithm atomic bit cctype climits cstddef cstdint cstdio cstdlib cstring cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new stdexcept string string_view tuple type_traits typeinfo utility version
typeinfo 7
cstddef cstdint cstdlib exception limits type_traits version
tuple 13
cstddef cstdint cstdlib cstring exception initializer_list iosfwd limits new type_traits typeinfo utility version
ciso646 0
any 18
atomic cstddef cstdint cstdlib cstring exception initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
system_error 28
algorithm atomic bit cctype cerrno cstddef cstdint cstdio cstdlib cstring cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new stdexcept string string_view tuple type_traits typeinfo utility version
ccomplex 44
algorithm atomic bit bitset cctype cerrno chrono climits cmath complex cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new ostream ratio sstream stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
map 22
algorithm atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new optional stdexcept tuple type_traits typeinfo utility version
shared_mutex 33
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
csignal 0
limits 3
cstddef type_traits version
ratio 5
climits cstddef cstdint type_traits version
fstream 45
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype deque exception filesystem functional initializer_list iomanip ios iosfwd istream iterator limits locale memory mutex new ostream ratio stack stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
optional 19
atomic cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
cfenv 0
ios 34
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list iosfwd iterator limits memory mutex new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility version
algorithm 20
atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
cstdbool 0
istream 40
algorithm atomic bit bitset cctype cerrno chrono climits cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd iterator limits locale memory mutex new ostream ratio stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
clocale 0
complex 43
algorithm atomic bit bitset cctype cerrno chrono climits cmath cstdarg cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype exception functional initializer_list ios iosfwd istream iterator limits locale memory mutex new ostream ratio sstream stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility version
list 21
algorithm atomic bit cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
iterator 13
cstddef cstdint cstdlib cstring exception initializer_list iosfwd limits new type_traits typeinfo utility version
string_view 22
algorithm atomic bit cstddef cstdint cstdio cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
regex 36
algorithm atomic bit cctype cerrno chrono climits cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype deque exception functional initializer_list iosfwd iterator limits memory mutex new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility vector version
queue 24
algorithm atomic bit climits cstddef cstdint cstdlib cstring deque exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility vector version
valarray 22
algorithm atomic bit cmath cstddef cstdint cstdlib cstring exception functional initializer_list iosfwd iterator limits memory new stdexcept tuple type_traits typeinfo utility version
また GCC9.3.0のC++17でも試したら、この様になりました（やっぱり長いので折りたたみ）
cctype 0
chrono 5
cstdint ctime limits ratio type_traits
ctime 0
vector 6
exception initializer_list new type_traits typeinfo utility
iomanip 29
array cctype cerrno clocale cstdint cstdio cstdlib ctime cwchar cwctype exception initializer_list ios iosfwd istream limits locale new ostream sstream stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility
cstdint 0
future 29
array atomic cctype cerrno chrono clocale condition_variable cstdint cstdio cstdlib ctime cwchar exception initializer_list iosfwd limits memory mutex new ratio stdexcept string string_view system_error thread tuple type_traits typeinfo utility
locale 24
array cctype cerrno clocale cstdint cstdio cstdlib ctime cwchar cwctype exception initializer_list iosfwd limits new stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility
string 15
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new string_view type_traits typeinfo
random 20
cctype cerrno clocale cmath cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new numeric string string_view type_traits typeinfo utility vector
condition_variable 24
array cctype cerrno chrono clocale cstdint cstdio cstdlib ctime cwchar exception initializer_list iosfwd limits new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility
cstddef 0
memory 20
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new stdexcept string string_view tuple type_traits typeinfo utility
functional 23
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new optional stdexcept string string_view tuple type_traits typeinfo unordered_map utility vector
cwctype 0
streambuf 18
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new stdexcept string string_view system_error type_traits typeinfo
cstring 0
cassert 0
numeric 1
type_traits
typeindex 1
typeinfo
cmath 2
limits type_traits
unordered_map 21
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new optional stdexcept string string_view tuple type_traits typeinfo utility
stack 7
deque exception initializer_list new type_traits typeinfo utility
cfloat 0
bit 2
limits type_traits
array 18
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new stdexcept string string_view type_traits typeinfo utility
utility 2
initializer_list type_traits
scoped_allocator 21
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits memory new stdexcept string string_view tuple type_traits typeinfo utility
type_traits 0
atomic 1
type_traits
codecvt 16
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new string string_view type_traits typeinfo
version 0
forward_list 5
exception initializer_list new type_traits typeinfo
thread 24
array cctype cerrno chrono clocale cstdint cstdio cstdlib ctime cwchar exception initializer_list iosfwd limits memory new ratio stdexcept string string_view tuple type_traits typeinfo utility
csetjmp 0
ctgmath 26
cctype cerrno clocale cmath complex cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream sstream stdexcept streambuf string string_view system_error type_traits typeinfo
stdexcept 16
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new string string_view type_traits typeinfo
cstdio 0
set 19
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new optional stdexcept string string_view type_traits typeinfo utility
mutex 24
array cctype cerrno chrono clocale cstdint cstdio cstdlib ctime cwchar exception initializer_list iosfwd limits new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility
iostream 23
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream stdexcept streambuf string string_view system_error type_traits typeinfo
filesystem 33
array cctype cerrno chrono clocale codecvt cstdint cstdio cstdlib ctime cwchar cwctype exception initializer_list iomanip ios iosfwd istream limits locale new ostream ratio sstream stdexcept streambuf string string_view system_error tuple type_traits typeinfo utility
charconv 4
cctype cerrno limits type_traits
exception 3
new type_traits typeinfo
unordered_set 21
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new optional stdexcept string string_view tuple type_traits typeinfo utility
new 3
exception type_traits typeinfo
ostream 21
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd limits new stdexcept streambuf string string_view system_error type_traits typeinfo
variant 7
exception initializer_list limits new type_traits typeinfo utility
memory_resource 29
array cctype cerrno chrono clocale condition_variable cstddef cstdint cstdio cstdlib ctime cwchar exception initializer_list iosfwd limits memory new ratio shared_mutex stdexcept string string_view system_error tuple type_traits typeinfo utility vector
climits 0
cstdlib 0
cstdarg 0
iosfwd 1
cwchar
cwchar 0
cerrno 0
cinttypes 1
cstdint
deque 6
exception initializer_list new type_traits typeinfo utility
sstream 23
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream stdexcept streambuf string string_view system_error type_traits typeinfo
initializer_list 0
bitset 16
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new string string_view type_traits typeinfo
typeinfo 0
tuple 19
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new stdexcept string string_view type_traits typeinfo utility
ciso646 0
any 6
exception initializer_list new type_traits typeinfo utility
system_error 17
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new stdexcept string string_view type_traits typeinfo
ccomplex 26
cctype cerrno clocale cmath complex cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream sstream stdexcept streambuf string string_view system_error type_traits typeinfo
map 21
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new optional stdexcept string string_view tuple type_traits typeinfo utility
shared_mutex 25
array cctype cerrno chrono clocale condition_variable cstdint cstdio cstdlib ctime cwchar exception initializer_list iosfwd limits new ratio stdexcept string string_view system_error tuple type_traits typeinfo utility
csignal 0
limits 0
cstdalign 0
ratio 2
cstdint type_traits
fstream 23
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream stdexcept streambuf string string_view system_error type_traits typeinfo
optional 18
cctype cerrno clocale cstdint cstdio cstdlib cwchar exception initializer_list iosfwd limits new stdexcept string string_view type_traits typeinfo utility
cfenv 0
ios 20
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list iosfwd limits new stdexcept streambuf string string_view system_error type_traits typeinfo
algorithm 24
array cctype cerrno clocale cstdint cstdio cstdlib cwchar exception functional initializer_list iosfwd limits new optional stdexcept string string_view tuple type_traits typeinfo unordered_map utility vector
cstdbool 0
istream 22
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd limits new ostream stdexcept streambuf string string_view system_error type_traits typeinfo
clocale 0
complex 25
cctype cerrno clocale cmath cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream sstream stdexcept streambuf string string_view system_error type_traits typeinfo
list 5
exception initializer_list new type_traits typeinfo
cuchar 1
cwchar
iterator 23
cctype cerrno clocale cstdint cstdio cstdlib cwchar cwctype exception initializer_list ios iosfwd istream limits new ostream stdexcept streambuf string string_view system_error type_traits typeinfo
string_view 6
cstdint cwchar initializer_list iosfwd limits type_traits
regex 47
algorithm array bitset cctype cerrno chrono clocale condition_variable cstddef cstdint cstdio cstdlib cstring ctime cwchar cwctype deque exception functional initializer_list ios iosfwd istream iterator limits locale map memory memory_resource new optional ostream ratio shared_mutex sstream stack stdexcept streambuf string string_view system_error tuple type_traits typeinfo unordered_map utility vector
queue 8
deque exception initializer_list new type_traits typeinfo utility vector
valarray 26
algorithm array cctype cerrno clocale cmath cstdint cstdio cstdlib cwchar exception functional initializer_list iosfwd limits new optional stdexcept string string_view tuple type_traits typeinfo unordered_map utility vector
標準ライブラリヘッダを全て include するのに必要な、最低限のヘッダを求める
どうやって求めるべきかは、この競プロの問題を参考にします。このH問題「include」が該当する問題です。
JAG 2021年度模擬地区予選問題 解説
解くにあたって、競プロなどをしていないと知らないようなテクニックが使用されますが、参加チームのほぼ全てのチームが解いているので、ICPC アジア地区に参加するレベルの参加者では皆知っているようなものです[要出典]。
（競技プログラミングは標準ライブラリヘッダを最低限の数のincludeで済ませたいときに役に立つ！🤔）
これを元に求めると、clang 10.0.0 の C++17 では、以下の31ヘッダを include することで、標準ライブラリヘッダを全て include することができることが分かりました。
[00] cassert
[00] cfenv
[00] cfloat
[00] ciso646
[00] clocale
[00] csetjmp
[00] csignal
[00] cstdbool
[01] cinttypes
[06] charconv
[13] typeindex
[18] any
[18] scoped_allocator
[21] forward_list
[21] list
[22] map
[22] set
[22] valarray
[22] variant
[23] unordered_map
[23] unordered_set
[24] queue
[33] condition_variable
[33] shared_mutex
[34] codecvt
[35] future
[36] regex
[41] iostream
[44] random
[45] ctgmath
[45] fstream
先頭の [nn] は、そのヘッダが何個の標準ライブラリヘッダをincludeしているのかを表しています。fstream は45個と、半分以上の標準ライブラリヘッダをincludeしているようです。
同様に GCC9.3.0 の C++17 でも試したら、以下のようになりました
[00] cassert
[00] cfenv
[00] cfloat
[00] ciso646
[00] climits
[00] csetjmp
[00] csignal
[00] cstdalign
[00] cstdarg
[00] cstdbool
[00] version
[01] cinttypes
[01] cuchar
[01] typeindex
[02] bit
[04] charconv
[05] forward_list
[05] list
[06] any
[07] variant
[08] queue
[19] set
[20] random
[21] scoped_allocator
[21] unordered_set
[23] fstream
[23] iostream
[26] ccomplex
[26] ctgmath
[26] valarray
[29] future
[33] filesystem
[47] regex
regex を include するだけで、実に47ヘッダもincludeされます。凄いですね…。
各コンパイラ・言語バージョンで試してみた結果は以下のとおりです。
Clang 10.0.0 / C++14
[00] cassert
[00] cfenv
[00] cfloat
[00] ciso646
[00] clocale
[00] csetjmp
[00] csignal
[00] cstdbool
[01] cinttypes
[12] typeindex
[17] scoped_allocator
[19] array
[19] forward_list
[19] list
[19] map
[19] set
[20] unordered_map
[20] unordered_set
[20] valarray
[22] queue
[30] condition_variable
[31] codecvt
[32] future
[33] regex
[38] iostream
[41] fstream
[41] random
[42] ctgmath
GCC 9.3.0 / C++14
[00] cassert
[00] cfenv
[00] cfloat
[00] ciso646
[00] climits
[00] csetjmp
[00] csignal
[00] cstdalign
[00] cstdarg
[00] cstdbool
[00] cstddef
[01] cinttypes
[01] cuchar
[01] typeindex
[05] forward_list
[05] list
[05] set
[07] queue
[10] valarray
[14] codecvt
[18] functional
[18] random
[19] scoped_allocator
[19] unordered_map
[19] unordered_set
[21] fstream
[21] iostream
[24] ccomplex
[24] ctgmath
[27] iomanip
[28] future
[37] regex
GCC 9.3.0 / C++14
[00] cassert
[00] cfloat
[00] ciso646
[00] climits
[00] csetjmp
[00] csignal
[00] cstdarg
[00] cstddef
[00] cstring
[00] functional
[00] limits
[00] numeric
[00] typeinfo
[02] list
[02] map
[02] memory
[02] set
[03] queue
[03] stack
[06] valarray
[07] bitset
[08] iomanip
[11] locale
[13] iostream
[13] iterator
[15] complex
[15] fstream
終わりに
いかがだったでしょうか？
<bits/stdc++.h> が無い環境用に88個のヘッダを書かなくても、30個程度のヘッダを書けば良さそうということが分かりました。ぜひご活用ください！
良ければ記事の LGTM・ストックお願いします！
え、競技プログラマはテンプレヘッダの長さを気にしない…？