[global.functions]

# 16 Library introduction [[library]](./#library)

## 16.4 Library-wide requirements [[requirements]](requirements#global.functions)

### 16.4.6 Conforming implementations [[conforming]](conforming#global.functions)

#### 16.4.6.4 Non-member functions [global.functions]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3645)

It is unspecified whether any
non-member
functions in the C++ standard library are defined as[inline](dcl.inline "9.2.8 The inline specifier [dcl.inline]")[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3651)

A call to a non-member function signature
described in [[support]](support "17 Language support library") through [[exec]](exec "33 Execution control library") and[[depr]](depr "Annex D (normative) Compatibility features") shall behave as if the implementation declared no additional
non-member function signatures[.](#2.sentence-1)[155](#footnote-155 "A valid C++ program always calls the expected library non-member function. An implementation can also define additional non-member functions that would otherwise not be called by a valid C++ program.")

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3663)

An implementation shall not declare a non-member function signature
with additional default arguments[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3667)

Unless otherwise specified,
calls made by functions in the standard library to non-operator, non-member functions
do not use functions from another namespace which are found through
argument-dependent name lookup ([[basic.lookup.argdep]](basic.lookup.argdep "6.5.4 Argument-dependent name lookup"))[.](#4.sentence-1)

[*Note [1](#note-1)*:

The phrase “unless otherwise specified” applies to cases such as
the swappable with requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))[.](#4.sentence-2)

The exception for overloaded operators allows argument-dependent lookup
in cases like that of[ostream_iterator​::​operator=](ostream.iterator.ops#lib:ostream_iterator,operator= "24.6.3.3 Operations [ostream.iterator.ops]"):

*Effects*: **out_stream* << value;if (*delim* != 0)**out_stream* << *delim*;return *this;

— *end note*]

[155)](#footnote-155)[155)](#footnoteref-155)

A valid C++ program always
calls the expected library non-member function[.](#footnote-155.sentence-1)

An implementation can
also define additional non-member functions that would otherwise not
be called by a valid C++ program[.](#footnote-155.sentence-2)