Storage duration specifiers

From Cppreference

C++ Standard Library
Language Utilities library Strings library Containers library Algorithms library Iterators library Numerics library Input/output library Localizations library Regular expressions library (C++11) Atomic operations library (C++11) Thread support library (C++11)
C++ language
General topics Preprocessor Keywords ASCII chart Escape sequences Flow control if statement switch statement for loop for loop on a range (C++11) while loop do-while loop continue statement break statement return statement Functions declaring functions exception specifications noexcept specifier inline specifier Exceptions throw expression try-catch block Namespaces declaring namespaces namespace aliales Types fundamental types compound types function types decltype specifier Specifiers cv specifiers storage duration specifiers constexpr specifier auto specifier Operators operators operator precedence alternative representations Utilities standard conversions static_cast conversion dynamic_cast conversion const_cast conversion reinterpret_cast conversion new expression delete expression typedef declaration type alias declaration attributes Classes declaring classes access specifiers granting access for non-members initializer_list Special member functions default constructor copy constructor move constructor assignment operator move operator destructor

• auto - automatic storage duration. (deprecated)
• register - automatic storage duration. Also hints to the compiler to place the variable in the processor's register. (deprecated)
• static - static storage duration and internal linkage
• extern - static storage duration and external linkage
• thread_local - thread local storage duration. (C++11 feature)

Contents 1 Explanation 1.1 Storage duration 1.2 Linkage 2 Keywords 3 Example

[edit] Explanation

[edit] Storage duration

All variables in a program have one of the following storage duration:

• automatic storage duration. The variable is allocated at the beginning of the enclosing code block and deallocated on end. All non-global variables have this storage duration, except those declared static, extern or thread_local.

• static storage duration. The variable is allocated when the program begins and deallocated when the program ends. Only one instance of the variable exists. All global variables have this storage duration, plus those declared with static or extern.

• thread local storage duration (C++11 feature). The variable is allocated when the thread begins and deallocated when the thread ends. Each thread has its own instance of the variable. Only variables declared thread_local have this storage duration.

• dynamic storage duration. The variable is allocated and deallocated per request by using dynamic memory allocation functions.

[edit] Linkage

The linkage refers to the ability of a variable to be referred to in other scopes. If the variable is declared in several scopes, but it can not be referred to from all of them, several instances of the variable are generated. The following linkages are recognized:

• no linkage. The variable can be referred to only from the scope they are in. All variables with automatic, thread local and dynamic storage durations have this linkage.

• internal linkage. The variable can be referred to from all scopes in the current translation unit. All variables with static storage duration which are either declared static, or const but not extern, have this linkage.

• external linkage. The variable can be referred to from the scopes in the other translation units. All variables with static storage duration have this linkage, except those declared static, or const but not extern.

[edit] Keywords

auto, register, static, extern, thread_local

[edit] Example

This section is incomplete