# Extra Clang Tools 22.1.2 documentation

## clang-tidy - bugprone-stringview-nullptr

# bugprone-stringview-nullptr

Checks for various ways that the `const CharT*` constructor of `std::basic_string_view` can be passed a null argument and replaces them with the default constructor in most cases. For the comparison operators, braced initializer list does not compile so instead a call to `.empty()` or the empty string literal are used, where appropriate.

This prevents code from invoking behavior which is unconditionally undefined. The single-argument `const CharT*` constructor does not check for the null case before dereferencing its input. The standard is slated to add an explicitly-deleted overload to catch some of these cases: wg21.link/p2166

To catch the additional cases of `NULL` (which expands to `__null`) and `0`, first run the `modernize-use-nullptr` check to convert the callers to `nullptr`.

    std::string_view sv = nullptr;

    sv = nullptr;

    bool is_empty = sv == nullptr;
    bool isnt_empty = sv != nullptr;

    accepts_sv(nullptr);

    accepts_sv({{}});  // A

    accepts_sv({nullptr, 0});  // B

is translated into…

    std::string_view sv = {};

    sv = {};

    bool is_empty = sv.empty();
    bool isnt_empty = !sv.empty();

    accepts_sv("");

    accepts_sv("");  // A

    accepts_sv({nullptr, 0});  // B

Note

The source pattern with trailing comment “A” selects the `(const CharT*)` constructor overload and then value-initializes the pointer, causing a null dereference. It happens to not include the `nullptr` literal, but it is still within the scope of this ClangTidy check.

Note

The source pattern with trailing comment “B” selects the `(const CharT*, size_type)` constructor which is perfectly valid, since the length argument is `0`. It is not changed by this ClangTidy check.