# Extra Clang Tools 21.1.8 documentation

## clang-tidy - modernize-replace-auto-ptr

# modernize-replace-auto-ptr

This check replaces the uses of the deprecated class `std::auto_ptr` by `std::unique_ptr` (introduced in C++11). The transfer of ownership, done by the copy-constructor and the assignment operator, is changed to match `std::unique_ptr` usage by using explicit calls to `std::move()`.

Migration example:

    -void take_ownership_fn(std::auto_ptr<int> int_ptr);
    +void take_ownership_fn(std::unique_ptr<int> int_ptr);

     void f(int x) {
    -  std::auto_ptr<int> a(new int(x));
    -  std::auto_ptr<int> b;
    +  std::unique_ptr<int> a(new int(x));
    +  std::unique_ptr<int> b;

    -  b = a;
    -  take_ownership_fn(b);
    +  b = std::move(a);
    +  take_ownership_fn(std::move(b));
     }

Since `std::move()` is a library function declared in `<utility>` it may be necessary to add this include. The check will add the include directive when necessary.

## Known Limitations

- If headers modification is not activated or if a header is not allowed to be changed this check will produce broken code (compilation error), where the headers’ code will stay unchanged while the code using them will be changed.

- Client code that declares a reference to an `std::auto_ptr` coming from code that can’t be migrated (such as a header coming from a 3rd party library) will produce a compilation error after migration. This is because the type of the reference will be changed to `std::unique_ptr` but the type returned by the library won’t change, binding a reference to `std::unique_ptr` from an `std::auto_ptr`. This pattern doesn’t make much sense and usually `std::auto_ptr` are stored by value (otherwise what is the point in using them instead of a reference or a pointer?).

     // <3rd-party header...>
     std::auto_ptr<int> get_value();
     const std::auto_ptr<int> & get_ref();

     // <calling code (with migration)...>
    -std::auto_ptr<int> a(get_value());
    +std::unique_ptr<int> a(get_value()); // ok, unique_ptr constructed from auto_ptr

    -const std::auto_ptr<int> & p = get_ptr();
    +const std::unique_ptr<int> & p = get_ptr(); // won't compile

- Non-instantiated templates aren’t modified.

    template <typename X>
    void f() {
        std::auto_ptr<X> p;
    }

    // only 'f<int>()' (or similar) will trigger the replacement.

## Options

IncludeStyle

  A string specifying which include-style is used, llvm or google. Default is llvm.