Modules (since C++20)

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function declaration
inline specifier
Exception specifications (until C++20)
noexcept specifier (C++11)
Exceptions
throw-expression	try-catch block
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Compound types Union types
Specifiers
decltype (C++11) auto (C++11) alignas (C++11)	const/volatile constexpr (C++11)
Storage duration specifiers
Initialization
Default initialization Value initialization Zero initialization Copy initialization Direct initialization	Aggregate initialization List initialization (C++11) Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions - Explicit conversions
static_cast - dynamic_cast
const_cast - reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
Special member functions
Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

Basic Concepts

language keywords

phases of translation

comments

the main() function

names and identifiers

types

fundamental types

objects

scope

object lifetime

storage duration and linkage

definitions and ODR

name lookup

qualified name lookup

unqualified name lookup

the as-if rule

undefined behavior

memory model

 

Modules help divide large amounts of code into logical parts.

Modules are orthogonal to namespaces.

// helloworld.cpp
export module helloworld;  // module declaration
import <iostream>;         // import declaration
 
export void hello() {      // export declaration
    std::cout << "Hello world!\n";
}

// main.cpp
import helloworld;  // import declaration
 
int main() {
    hello();
}

Syntax

export(optional) module module-name module-partition(optional) attr(optional) ;	(1)
export declaration	(2)
export { declaration-seq(optional) }	(3)
export(optional) import module-name attr(optional) ;	(4)
export(optional) import module-partition attr(optional) ;	(5)
export(optional) import header-name attr(optional) ;	(6)
module ;	(7)
module : private ;	(8)

1) Module declaration. Declares that the current translation unit is a module unit.

2,3) Export declaration. Export all namespace-scope declarations in declaration or declaration-seq.

4,5,6) Import declaration. Import a module unit/module partition/header unit.

7) Starts a global module fragment.

8) Starts a private module fragment.

Keywords

export, import, module