The set of all global variables is known as the global environment or global state. Computers commonly provide direct, efficient access to the program's global variables and to the local variables of only the current innermost procedure or function, the topmost stack frame While the use of global variables is generally discouraged in modern programming, some older operating systems such as unix were originally designed for uniprocessor hardware and often use global variables to store important values
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An example is the errno used by many functions of the c library
On a modern machine, where multiple threads may be modifying the errno variable, a call of a.
The dynamic loader calculates the address referred to by a global variable and stores the value in such global variable Pages with code and pages with global variables that do not contain pointers to code or global data remain shared between processes. Global variables accessible by a in the scope of m In particular, an object should avoid invoking methods of an object returned by another method
[6] that is, the code a.m().n() breaks the law where a.m() does not. For example, the use of global variables is generally deemed unwise, because it adds coupling between all callables that use the global variables If such coupling is not necessary, they advise to refactor callables to accept passed parameters instead. Global optimization is a branch of operations research, applied mathematics, and numerical analysis that attempts to find the global minimum or maximum of a function or a set of functions on a given set.
This has advantages and disadvantages
A disadvantage is that local variables within the protothread cannot be trusted to have retained their values across a yield to another context They must retain their state through the use of static or external, often global, variables
