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See subject. What were they thinking?
UPDATE: Changed from "static" to "internal linkage" to save confusion.
To give an example... Putting the following in a file:
const int var_a = 1; int var_b = 1; ...and compiling with g++ -c test.cpp only exports var_b.
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The qualifier const can be applied to the declaration of any variable to specify that its value will not be changed ( Which depends upon where const variables are stored, we may change the value of const variable by using pointer ).
Internal Linkage: An identifier implementing internal linkage is not accessible outside the translation unit it is declared in. Any identifier within the unit can access an identifier having internal linkage. It is implemented by the keyword static .
Yes. const is there in C, from C89.
Although constexpr variables can be given external linkage via the extern keyword, they can not be forward declared, so there is no value in giving them external linkage. This is because the compiler needs to know the value of the constexpr variable (at compile time).
I believe you mean
Why does const imply internal linkage in C++
It's true that if you declare a const object at namespace scope, then it has internal linkage.
Appendix C (C++11, C.1.2) gives the rationale
Change: A name of file scope that is explicitly declared const, and not explicitly declared extern, has internal linkage, while in C it would have external linkage
Rationale: Because const objects can be used as compile-time values in C++, this feature urges programmers to provide explicit initializer values for each const. This feature allows the user to put const objects in header files that are included in many compilation units.
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