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c++c++11language-lawyerstandards-compliance

Is "auto int i" valid C++11?


In answering this question the question arose as to whether the traditional C meaning of the keyword auto (automatic, rather than static or extern storage) is still valid in C++11 now that it means type deduction.

I remember that the old meaning of auto should remain where relevant but others disagreed.

auto char c = 42; // either compilation error or c = '*'

Looking at compilers I see the current division.

  1. Old meaning of auto is no longer allowed
  • VS10
  • g++
  1. Old meaning of auto is used where relevant

Do you know which is the correct behaviour?


Solution

  • No, it is not. In fact, §7.1.6.​4/3 gives the following example:

    auto x = 5; // OK: x has type int
    const auto *v = &x, u = 6; // OK: v has type const int*, u has type const int
    static auto y = 0.0; // OK: y has type double
    auto int r; // error: auto is not a storage-class-specifier
    

    As you can see, it results in an error. §7.1.6.​5 pretty much seals the deal with:

    A program that uses auto in a context not explicitly allowed in this section is ill-formed.