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An environment variable is a user-definable value that can affect the way running processes will behave on a computer. Environment variables are part of the ...
Environment variables are a facility provided by some operating systems.Within the OS's shell (ksh in Unix, bash in Linux, COMMAND.COM in DOS and CMD.EXE in Windows) they are a kind of variable: for instance, in unix and related systems an ordinary variable becomes an environment variable when the export keyword is used.
The runtime environment includes not only accessible state values, but also active entities with which the program can interact during execution. For example, environment variables are features of many operating systems, and are part of the runtime environment; a running program can access them via the runtime system. Likewise, hardware devices ...
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
C++11 introduces the thread_local [3] keyword which can be used in the following cases Namespace level (global) variables; File static variables; Function static variables; Static member variables; Aside from that, various compiler implementations provide specific ways to declare thread-local variables:
An external variable can be accessed by all the functions in all the modules of a program. It is a global variable.For a function to be able to use the variable, a declaration or the definition of the external variable must lie before the function definition in the source code.
That way, a nested call can modify its local variables without affecting any of the suspended calls variables. Recursion allows direct implementation of functionality defined by mathematical induction and recursive divide and conquer algorithms. Here is an example of a recursive function in C/C++ to find Fibonacci numbers:
Local variables are destroyed when the local block or function that they are declared in is closed. C++ destructors for local variables are called at the end of the object lifetime, allowing a discipline for automatic resource management termed RAII, which is widely used in C++. Member variables are created when the parent object is created.