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In computer programming, a static variable is a variable that has been allocated "statically", meaning that its lifetime (or "extent") is the entire run of the program. This is in contrast to shorter-lived automatic variables, whose storage is stack allocated and deallocated on the call stack; and in contrast to dynamically allocated objects, whose storage is allocated and deallocated in heap ...
static is a reserved word in many programming languages to modify a declaration. The effect of the keyword varies depending on the details of the specific programming language, most commonly used to modify the lifetime (as a static variable) and visibility (depending on linkage), or to specify a class member instead of an instance member in classes.
This shows the typical layout of a simple computer's program memory with the text, various data, and stack and heap sections. The data segment contains initialized static variables, i.e. global variables and local static variables which have a defined value and can be modified.
The different types of variables are static, stack-dynamic, explicit heap-dynamic, and implicit heap-dynamic. A static variable is also known as global variable, it is bound to a memory cell before execution begins and remains to the same memory cell until termination. A typical example is the static variables in C and C++.
The static keyword (static and extern are mutually exclusive), applied to the definition of an external variable, changes this a bit: the variable can only be accessed by the functions in the same module where it was defined. But it is possible for a function in the same module to pass a reference (pointer) of the variable to another function ...
Hence all variables are in the scope of either a class or a method. In Java, static fields (also known as class variables) exist independently of any instances of the class and one copy is shared among all instances; hence public static fields are used for many of the same purposes as global variables in other languages because of their similar ...
In the C programming language, each thread has its own stack. However, a static variable is not kept on the stack; all threads share simultaneous access to it. If multiple threads overlap while running the same function, it is possible that a static variable might be changed by one thread while another is midway through checking it.
The application programming interface (API) function TlsAlloc can be used to obtain an unused TLS slot index; the TLS slot index will then be considered 'used'.. The TlsGetValue and TlsSetValue functions are then used to read and write a memory address to a thread-local variable identified by the TLS slot index.