The set of all global variables is known as the global environment or global state. In computer science, a local variable is a variable that is given local scope A local variable reference in the function or block in which it is declared overrides the same variable name in the larger scope In programming languages with only two levels of visibility, local variables are contrasted with global variables A global variable is a variable declared in the main body of the source code, outside all functions, while a local variable is one declared within the body of a function or a block. External variable in the c programming language, and its predecessor b, an external variable is a variable defined outside any function block
On the other hand, a local (automatic) variable is a variable defined inside a function block. Variable lifetime is contrasted with scope (where a variable can be used) Global and local refer to scope, not lifetime, but scope often implies lifetime In many languages, global variables are always static, but in some languages they are dynamic, while local variables are generally automatic, but may be static. While the term can refer to global variables, it is primarily used in the context of nested and anonymous functions where some variables can be in neither the local nor the global scope. In compiler optimization, register allocation is the process of assigning local automatic variables and expression results to a limited number of processor registers
