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- whose declaration contains the storage-class specifier extern, where no prior declaration of that identifier is visible.*
- for a function whose declaration contains no storage-class specifier.
- for an object with file scope whose declaration contains no storage-class specifier.
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- An identifier declared to be anything other than an object or a function.
- An identifier declared to be a function parameter.
- A block scope identifier for an object declared without the storage-class specifier extern.
(* If a prior declaration is visible and has no linkage, the latter declaration is externally linked.
If a prior declaration is visible and has either internal or external linkage, the latter declaration is classified with the same linkage as the prior declaration.)
Use of an identifier (within one translational unit) classified as both internally and externally linked causes undefined behavior. A translational unit includes the sourcefile together with its headers, and all sourcefiles included via the preprocessing directive #include.
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