CODEWITHSUNDEEP
c++c++14language-lawyerstdstringnullptr
iammilind
iammilind

Reputation: 69968

Why is assignment of 0 or nullptr to std::string allowed, even when it results in a straight forward runtime exception?

std::string s = 0;  // = nullptr ---> throws `std::logic_error`

Above statement results in segmentation fault. Why is it allowed?
[At least the constructor overload of nullptr should have been =delete, isn't it?]

Upvotes: 1

Views: 725

Answers (2)

iammilind
iammilind

Reputation: 69968

For C++23, constructing std::string or std::string_view from nullptr/NULL/0 is forbidden

A Proposal to Prohibit std::basic_string and std::basic_string_view construction from nullptr.

Though one may not use string s = nullptr in practice, it may get triggered sometimes unintentionally in a generic code. e.g.

template<typename T>
struct X {
  ...
  T t = 0;
  ...
};

X<int> xi; // ok
X<float> xf; // ok
X<string> xs; // c++20 = runtime assert? --- c++23 = compiler error!

Upvotes: 5

Bathsheba
Bathsheba

Reputation: 234635

In that case, the constructor to a const char* is called due to the way overload resolution works.

And if that pointer is nullptr then the standard library attempts to dereference a null pointer value with undefined results.

std::string is already hideously bloated. My guess is that nobody has managed to convince the C++ standards committee of the merits of having a std::string(std::nullptr_t) constructor.

Upvotes: 3

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