The set of all global variables is known as the global environment or global state. Additionally, they permit lazy allocation and initialization, whereas global variables in many languages will always consume resources Process environment block in computing the process environment block (abbreviated peb) is a data structure in the windows nt operating system family
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It is an opaque data structure that is used by the operating system internally, most of whose fields are not intended for use by anything other than the operating system
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 Or there must be a declaration of the variable, with the keyword extern, inside the function System functions (previously known as global variables) are distinguished by a @@ prefix
The scope of temporary tables is indicated by the prefix # designating local and ## designating global In windows powershell, which was partly inspired by unix shells and perl, variable names are prefixed by the $ sigil. Environment variables are part of the environment in which a process runs. A second use case would be multiple threads accumulating information into a global variable
To avoid a race condition, every access to this global variable would have to be protected by a mutex.
Singletons are often preferred to global variables because they do not pollute the global namespace (or their containing namespace)
