1. | An implementation shall support input files
that are a sequence of UTF-8 code units (UTF-8 files). It may also support
an implementation-defined set of other kinds of input files, and,
if so, the kind of an input file is determined in
an implementation-defined manner
that includes a means of designating input files as UTF-8 files,
independent of their content.
If an input file is determined to be a UTF-8 file,
then it shall be a well-formed UTF-8 code unit sequence and
it is decoded to produce a sequence of Unicode8
scalar values. A sequence of translation character set elements is then formed
by mapping each Unicode scalar value
to the corresponding translation character set element. In the resulting sequence,
each pair of characters in the input sequence consisting of
U+000d carriage return followed by U+000a line feed,
as well as each
U+000d carriage return not immediately followed by a U+000a line feed,
is replaced by a single new-line character. For any other kind of input file supported by the implementation,
characters are mapped, in an
implementation-defined manner,
to a sequence of translation character set elements ([lex.charset]),
representing end-of-line indicators as new-line characters. |
2. | Each sequence of a backslash character (\)
immediately followed by
zero or more whitespace characters other than new-line followed by
a new-line character is deleted, splicing
physical source lines to form logical source lines. Only the last
backslash on any physical source line shall be eligible for being part
of such a splice. [Note 2: — end note]
A source file that is not empty and that (after splicing)
does not end in a new-line character
shall be processed as if an additional new-line character were appended
to the file. |
3. | The source file is decomposed into preprocessing
tokens ([lex.pptoken]) and sequences of whitespace characters
(including comments).
Each comment ([lex.comment]) is replaced by one space character. New-line characters are
retained. Whether each nonempty sequence of whitespace characters other
than new-line is retained or replaced by one space character is
unspecified. As characters from the source file are consumed
to form the next preprocessing token
(i.e., not being consumed as part of a comment or other forms of whitespace),
except when matching a
c-char-sequence,
s-char-sequence,
r-char-sequence,
h-char-sequence, or
q-char-sequence,
universal-character-names are recognized ([lex.universal.char]) and
replaced by the designated element of the translation character set ([lex.charset]). The process of dividing a source file's
characters into preprocessing tokens is context-dependent. [Example 1: — end example] |
4. | Preprocessing directives ([cpp]) are executed, macro invocations are
expanded ([cpp.replace]), and _Pragma unary operator expressions are executed ([cpp.pragma.op]). A #include preprocessing directive ([cpp.include]) causes the named header or
source file to be processed from phase 1 through phase 4, recursively. All preprocessing directives are then deleted. |
5. | For a sequence of two or more adjacent string-literal tokens,
a common encoding-prefix is determined
as specified in [lex.string]. |
6. | |
7. | Whitespace characters separating tokens are no longer
significant. Each preprocessing token is converted into a
token ([lex.token]). The resulting tokens
constitute a translation unit and
are syntactically and
semantically analyzed and translated. [Note 3: The process of analyzing and translating the tokens can occasionally
result in one token being replaced by a sequence of other
tokens ([temp.names]). — end note]
It is
implementation-defined
whether the sources for
module units and header units
on which the current translation unit has an interface
dependency ([module.unit], [module.import])
are required to be available. [Note 4: Source files, translation
units and translated translation units need not necessarily be stored as
files, nor need there be any one-to-one correspondence between these
entities and any external representation. The description is conceptual
only, and does not specify any particular implementation. — end note] |
8. | Translated translation units and instantiation units are combined
as follows:
Each translated translation unit is examined to
produce a list of required instantiations. [Note 6: This can include
instantiations which have been explicitly
requested ([temp.explicit]). — end note]
The definitions of the
required templates are located. It is implementation-defined whether the
source of the translation units containing these definitions is required
to be available.
All the required instantiations
are performed to produce
instantiation units.
The
program is ill-formed if any instantiation fails. |
9. |
character | glyph | ||
U+0009 | character tabulation | ||
U+000b | line tabulation | ||
U+000c | form feed | ||
U+0020 | space | ||
U+000a | line feed | new-line | |
U+0021 | exclamation mark | ! | |
U+0022 | quotation mark | " | |
U+0023 | number sign | # | |
U+0024 | dollar sign | $ | |
U+0025 | percent sign | % | |
U+0026 | ampersand | & | |
U+0027 | apostrophe | ' | |
U+0028 | left parenthesis | ( | |
U+0029 | right parenthesis | ) | |
U+002a | asterisk | * | |
U+002b | plus sign | + | |
U+002c | comma | , | |
U+002d | hyphen-minus | - | |
U+002e | full stop | . | |
U+002f | solidus | / | |
U+0030 .. U+0039 | digit zero .. nine | 0 1 2 3 4 5 6 7 8 9 | |
U+003a | colon | : | |
U+003b | semicolon | ; | |
U+003c | less-than sign | < | |
U+003d | equals sign | = | |
U+003e | greater-than sign | > | |
U+003f | question mark | ? | |
U+0040 | commercial at | @ | |
U+0041 .. U+005a | latin capital letter a .. z | A B C D E F G H I J K L M | |
N O P Q R S T U V W X Y Z | |||
U+005b | left square bracket | [ | |
U+005c | reverse solidus | \ | |
U+005d | right square bracket | ] | |
U+005e | circumflex accent | ^ | |
U+005f | low line | _ | |
U+0060 | grave accent | ` | |
U+0061 .. U+007a | latin small letter a .. z | a b c d e f g h i j k l m | |
n o p q r s t u v w x y z | |||
U+007b | left curly bracket | { | |
U+007c | vertical line | | | |
U+007d | right curly bracket | } | |
U+007e | tilde | ~ |
alignas | constinit | false | public | true | |
alignof | const_cast | float | register | try | |
asm | continue | for | reinterpret_cast | typedef | |
auto | co_await | friend | requires | typeid | |
bool | co_return | goto | return | typename | |
break | co_yield | if | short | union | |
case | decltype | inline | signed | unsigned | |
catch | default | int | sizeof | using | |
char | delete | long | static | virtual | |
char8_t | do | mutable | static_assert | void | |
char16_t | double | namespace | static_cast | volatile | |
char32_t | dynamic_cast | new | struct | wchar_t | |
class | else | noexcept | switch | while | |
concept | enum | nullptr | template | ||
const | explicit | operator | this | ||
consteval | export | private | thread_local | ||
constexpr | extern | protected | throw |
and | and_eq | bitand | bitor | compl | not | |
not_eq | or | or_eq | xor | xor_eq |
integer-literal other than decimal-literal | |||
none | int | int | |
long int | unsigned int | ||
long long int | long int | ||
unsigned long int | |||
long long int | |||
unsigned long long int | |||
u or U | unsigned int | unsigned int | |
unsigned long int | unsigned long int | ||
unsigned long long int | unsigned long long int | ||
l or L | long int | long int | |
long long int | unsigned long int | ||
long long int | |||
unsigned long long int | |||
Both u or U | unsigned long int | unsigned long int | |
and l or L | unsigned long long int | unsigned long long int | |
ll or LL | long long int | long long int | |
unsigned long long int | |||
Both u or U | unsigned long long int | unsigned long long int | |
and ll or LL | |||
z or Z | the signed integer type corresponding | the signed integer type | |
to std::size_t ([support.types.layout]) | corresponding to std::size_t | ||
std::size_t | |||
Both u or U | std::size_t | std::size_t | |
and z or Z |
Encoding | Kind | Type | Associated char- | Example | |
prefix | acter encoding | ||||
none | char | ordinary literal | 'v' | ||
multicharacter literal | int | encoding | 'abcd' | ||
L | wchar_t | wide literal | L'w' | ||
encoding | |||||
u8 | char8_t | UTF-8 | u8'x' | ||
u | char16_t | UTF-16 | u'y' | ||
U | char32_t | UTF-32 | U'z' |
character | |||
U+000a | line feed | \n | |
U+0009 | character tabulation | \t | |
U+000b | line tabulation | \v | |
U+0008 | backspace | \b | |
U+000d | carriage return | \r | |
U+000c | form feed | \f | |
U+0007 | alert | \a | |
U+005c | reverse solidus | \\ | |
U+003f | question mark | \? | |
U+0027 | apostrophe | \' | |
U+0022 | quotation mark | \" |
type | ||
none | double | |
f or F | float | |
l or L | long double | |
f16 or F16 | std::float16_t | |
f32 or F32 | std::float32_t | |
f64 or F64 | std::float64_t | |
f128 or F128 | std::float128_t | |
bf16 or BF16 | std::bfloat16_t |
Enco- | Kind | Type | Associated | Examples | |
ding | character | ||||
prefix | encoding | ||||
none | array of n const char | ordinary literal encoding | "ordinary string" R"(ordinary raw string)" | ||
L | array of n const wchar_t | wide literal encoding | L"wide string" LR"w(wide raw string)w" | ||
u8 | array of n const char8_t | UTF-8 | u8"UTF-8 string" u8R"x(UTF-8 raw string)x" | ||
u | array of n const char16_t | UTF-16 | u"UTF-16 string" uR"y(UTF-16 raw string)y" | ||
U | array of n const char32_t | UTF-32 | U"UTF-32 string" UR"z(UTF-32 raw string)z" |
Translation unit #1:export module Q; export int sq(int i) { return i*i; }
Translation unit #2:export module R; export import Q;
Translation unit #3:import R; int main() { return sq(9); } // OK, sq from module Q — end example]
Translation unit #1:export module M; namespace R { export struct X {}; export void f(X); } namespace S { export void f(R::X, R::X); }
Translation unit #2:export module N; import M; export R::X make(); namespace R { static int g(X); } export template<typename T, typename U> void apply(T t, U u) { f(t, u); g(t); }
Translation unit #3:module Q; import N; namespace S { struct Z { template<typename T> operator T(); }; } void test() { auto x = make(); // OK, decltype(x) is R::X in module M R::f(x); // error: R and R::f are not visible here f(x); // OK, calls R::f from interface of M f(x, S::Z()); // error: S::f in module M not considered // even though S is an associated namespace apply(x, S::Z()); // error: S::f is visible in instantiation context, but // R::g has internal linkage and cannot be used outside TU #2 } — end example]
"decls.h":int f(); // #1, attached to the global module int g(); // #2, attached to the global module
Module interface of M:module; #include "decls.h" export module M; export using ::f; // OK, does not declare an entity, exports #1 int g(); // error: matches #2, but attached to M export int h(); // #3 export int k(); // #4
Other translation unit:import M; static int h(); // error: matches #3 int k(); // error: matches #4 — end example]
Translation unit #1:export module A; static void f() {} inline void it() { f(); } // error: is an exposure of f static inline void its() { f(); } // OK template<int> void g() { its(); } // OK template void g<0>(); decltype(f) *fp; // error: f (though not its type) is TU-local auto &fr = f; // OK constexpr auto &fr2 = fr; // error: is an exposure of f constexpr static auto fp2 = fr; // OK struct S { void (&ref)(); } s{f}; // OK, value is TU-local constexpr extern struct W { S &s; } wrap{s}; // OK, value is not TU-local static auto x = []{f();}; // OK auto x2 = x; // error: the closure type is TU-local int y = ([]{f();}(),0); // error: the closure type is not TU-local int y2 = (x,0); // OK namespace N { struct A {}; void adl(A); static void adl(int); } void adl(double); inline void h(auto x) { adl(x); } // OK, but certain specializations are exposures
Translation unit #2:module A; void other() { g<0>(); // OK, specialization is explicitly instantiated g<1>(); // error: instantiation uses TU-local its h(N::A{}); // error: overload set contains TU-local N::adl(int) h(0); // OK, calls adl(double) adl(N::A{}); // OK; N::adl(int) not found, calls N::adl(N::A) fr(); // OK, calls f constexpr auto ptr = fr; // error: fr is not usable in constant expressions here } — end example]