Describe about storage allocation and scope of global, extern, static, local and register variables?

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Describe about storage allocation and scope of global, extern, static, local and register variables? 


Globals have application-scope. They’re available in any compilation unit that includes an appropriate declaration (usually brought from a header file). They’re stored wherever the linker puts them, usually a place called the “BSS segment.” Extern? This is essentially “global.” 

Static: Stored the same place as globals, typically, but only available to the compilation unit that contains them. If they are block-scope global, only available within that block and its subblocks. 

Local: Stored on the stack, typically. Only available in that block and its subblocks. (Although pointers to locals can be passed to functions invoked from within a scope where that local is valid.) 

Register: See tirade above on “local” vs. “register.” The only difference is that the C compiler will not let you take the address of something you’ve declared as “register.”

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