Constructing a vector<int> with 2 string literals

问题

For the following program:

#include <vector>
#include <iostream>

int main()
{
  std::vector<int> v = {"a", "b"};
  
  for(int i : v)
    std::cout << i << " ";   
}

clang prints 97 0. The ascii value of 'a' is 97, but I don't fully understand the output.

On the other hand, gcc throws an exception:

terminate called after throwing an instance of 'std::length_error'
  what():  cannot create std::vector larger than max_size()

so I assume it's using the 2 argument constructor that takes the size and default value, where the size is computed from the address of the string literal "a".

If the program is well-formed, what is the correct behavior? Here's the code.

回答1:

I assume it's using the 2 argument constructor that takes the size and default value

No, it's using the constructor taking two input iterators. "a" and "b" could decay to pointer which is valid iterator. As the pointer (iterator) to const char, the dereferenced const char would be converted to int and added as the vector's element. Anyway the code has UB because "a" and "b" don't refer to valid range, "b" is not reachable from "a".

来源：https://stackoverflow.com/questions/62835713/constructing-a-vectorint-with-2-string-literals