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c++c++-faq

What is external linkage and internal linkage?

I want to understand the external linkage and internal linkage and their difference.

I also want to know the meaning of

const variables internally link by default unless otherwise declared as extern.

Solution

  • When you write an implementation file (.cpp, .cxx, etc) your compiler generates a translation unit. This is the source file from your implementation plus all the headers you #included in it.

    Internal linkage refers to everything only in scope of a translation unit.

    External linkage refers to things that exist beyond a particular translation unit. In other words, accessible through the whole program, which is the combination of all translation units (or object files).