[cpp.scope]

# 15 Preprocessing directives [[cpp]](./#cpp)

## 15.7 Macro replacement [[cpp.replace]](cpp.replace#cpp.scope)

### 15.7.6 Scope of macro definitions [cpp.scope]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/preprocessor.tex#L2040)

A macro definition lasts
(independent of block structure)
until a corresponding#undef directive is encountered or
(if none is encountered)
until the end of the translation unit[.](#1.sentence-1)

Macro definitions have no significance after translation phase 4[.](#1.sentence-2)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/preprocessor.tex#L2050)

A preprocessing directive of the form

# undef [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]") [*new-line*](cpp.pre#nt:new-line "15.1 Preamble [cpp.pre]")

causes the specified identifier no longer to be defined as a macro name[.](#2.sentence-1)

It is ignored if the specified identifier is not currently defined as
a macro name[.](#2.sentence-2)