[global.functions]

A call to a non-member function signature described in [support] through [exec] and [depr] shall behave as if the implementation declared no additional non-member function signatures.147

An implementation shall not declare a non-member function signature with additional default arguments.

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]).

[Note 1:

The phrase “unless otherwise specified” applies to cases such as the swappable with requirements ([swappable.requirements]).

The exception for overloaded operators allows argument-dependent lookup in cases like that of ostream_iterator::operator=:

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

— end note]

147)147)

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.