About stdio.h header in C++ #Linux

C++におけるstdio.hヘッダについて

I wondered why I can use cstdio API with including only iostream.

iostreamをインクルードしただけでcstdioが使用可能になる点について疑問に思ったので調べてみました。

OSX (BSD)

I browsed c++ headers and found following path:

clang++-6.0

iostream -> ostream -> ios -> iosfwd -> wchar.h -> stdio.h

llvm-g++-4.2

iostream -> ostream -> ios -> iosfwd -> bits/c++io.h -> cstdio -> stdio.h

g++-mp-4.8

iostream -> ostream -> ios -> iosfwd -> bits/postypes.h -> cwchar -> wchar.h -> stdio.h

Also I have found this very interesting path:

clang++-6.0

queue -> vector -> memory -> iterator -> iosfwd

llvm-g++-4.2

queue -> vector -> bits/stl_algobase.h -> iosfwd
iterator -> ostream

g++-mp-4.8

iterator -> ostream

So, including iostream, ios or iterator is enough for stdio...

Linux (glibc)

Since glibc's stdio.h is guarded, the path is little bit different.

glibcのstdio.hはガードされているので、経路は少し異なります。

# 3.3
iostream -> ostream -> ios -> iosfwd -> bits/fpos.h -> bits/c++io.h -> cstdio -> stdio.h
# 3.4,4.1,4.2
iostream -> ostream -> ios -> iosfwd -> bits/c++io.h -> cstdio -> stdio.h
# 4.3
iostream -> ostream -> ios -> bits/char_traits.h -> cstdio -> stdio.h

The path iosfwd -> bits/c++io.h and bits/char_traits.h -> cstdio has disappeared from g++ 4.4.
That's why we need to include cstdio separately.

iosfwd -> bits/c++io.hおよびbits/char_traits.h -> cstdioの経路はg++ 4.4でなくなりました。
このためcstdioを別途インクルードしなければならないのです。

On the other hand,

iostream -> ostream -> ios -> __locale -> string -> cstdio -> stdio.h

this path is available (also on OSX). Really funny...
上記経路はLinuxにもOSXにも存在します。

Digression

以下余談。

MinGW

iostream -> ostream -> ios -> bits/localefwd.h -> bits/c++locale.h -> clocale -> locale.h -> stdio.h

wchar.h does not include stdio.h, but locale.h does...

Android NDK

stdio.h exists in include-fixed and it is not guarded, so the path of g++-mp-4.8 should be available. Confirmed with 4.4.3.

newlib

So firm, the implementation looks the wisest.
しっかりした作り。一番賢い実装な感じ。