29 Input/output library [input.output]

29.4 Standard iostream objects [iostream.objects]

29.4.2 Overview [iostream.objects.overview]

1
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In this Clause, the type name FILE refers to the type FILE declared in <cstdio> ([cstdio.syn]).
2
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The header <iostream> declares objects that associate objects with the standard C streams provided for by the functions declared in <cstdio>, and includes all the headers necessary to use these objects.
3
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The objects are constructed and the associations are established at some time prior to or during the first time an object of class ios_­base​::​Init is constructed, and in any case before the body of main begins execution.284
The objects are not destroyed during program execution.285
The results of including <iostream> in a translation unit shall be as if <iostream> defined an instance of ios_­base​::​Init with static storage duration.
4
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Mixing operations on corresponding wide- and narrow-character streams follows the same semantics as mixing such operations on FILEs, as specified in the C standard library.
5
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Concurrent access to a synchronized ([ios.members.static]) standard iostream object's formatted and unformatted input ([istream]) and output ([ostream]) functions or a standard C stream by multiple threads does not result in a data race ([intro.multithread]).
[ Note
:
Users must still synchronize concurrent use of these objects and streams by multiple threads if they wish to avoid interleaved characters.
— end note
 ]
See also: ISO C 7.21.2
284)
If it is possible for them to do so, implementations should initialize the objects earlier than required.
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285)
Constructors and destructors for objects with static storage duration can access these objects to read input from stdin or write output to stdout or stderr.
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