Is `std::istream_iterator<float>` reading out-of-range number undefined behavior?

const std::string str = "-5.73945e-39";
std::istringstream iss(str);
auto vals = std::vector<float>(std::istream_iterator<float>(iss), std::istream_iterator<float>{});

If I compile with Apple clang version 15.0.0 (clang-1500.0.16.10) on my M1 chip Mac, size of vals is 0, but if I compile with other compilers (using any c++ online playground), the size of vals is 1.

Apparently the value is out of float range. Anyone knows whether this is leading to undefined behavior? Thanks!

Local and online c++ playground compiling and running.

No, it is not undefined behavior. If the extraction operation on the stream fails, the failbit should be set, which can be examined by calling iss.fail(). When this failure occurs, it will also cause the iterator to become equal to the end iterator, stopping the extraction.

So, if there is a parse issue, the iteration will stop before the first invalid value, and you can check this by examining the failbit.

if (iss.fail() ) {
  std::cout << "Error occurred\n";
} else {
  // Successful path
} 

For a more comprehensive list of what each of the state bits mean, see https://en.cppreference.com/w/cpp/io/ios_base/iostate