C++ string - strange behaviour when using initialization list constructor

I know that I can use initialization list to fill a string. I also know that I can use a constructor with a count parameterer to insert null characters into string. But when I combine both... strange things happen.

It looks that the compiler makes some implicit promotion from int to initializer_list or allocator. But I don't know why it doesn't give me any warning and why it makes it implicit.

Could you explain to me what happens with strings s6, and s7?

http://ift.tt/1NRTctA

#include <iostream>
#include <string>
using namespace std;

class A{
};

int main() {

    // string::string(charT const* s)
    string s1("12345");
    // 5 - because constructor takes into account null-terminated character
    cout << s1.size() << endl;

    // string::string(charT const* s, size_type count)
    string s2("12345",3);
    // 3 - because the length of the string is taken from count parameter. 
    cout << s2.size()<<endl;

    string s3("12345",5);
    // 5 - because the length of the string is taken from count,  parameter. 
    cout << s3.size()<<endl;

    // string(std::initializer_list<charT> ilist)
    string s4({'1','2','3','4','5'});
    // 5 - because string is built from the contents of the initializer list init. 
    cout << s4.size()<<endl;

    // basic_string( std::initializer_list<CharT> init,const Allocator& alloc = Allocator() );
    // doesn't compile, no known conversion for argument 2 from 'A' to 'const std::allocator<char>&'
    //string s5({'1','2','3','4','5'},A());
    //cout << s5.size()<<endl;

    // basic_string( std::initializer_list<CharT> init,const Allocator& alloc = Allocator() );
    string s6({'1','2','3','4','5'},3);
    // 2 - why this compiles (with no warning) and what this result means?
    cout << s6.size() << endl;

    string s7({'1','2','3','4','5'},5);
    // 0 - why this compiles (with no warning) and what this result means?
    cout << s7.size()<<endl;

    return 0;
}