Extra zero char at end of string appears in C++ for range loop

Question

The following code

#include <iostream>
#include <string>
int main()
{
    std::string s = "abc";
    for (char c : s)
        std::cout << (int) c << " ";
}

prints "97 98 99 ".

The following code

#include <iostream>
int main()
{
    for (char c : "abc")
        std::cout << (int) c << " ";
}

prints "97 98 99 0 ".

Where is the extra 0 coming from in the second code?

Answer 1

The literal "abc" is a const char[4] type: the final element is the NUL terminator (with value 0).

In the second snippet, the value of the NUL terminator is printed as the code is describing an iteration over that entire const char[4] array.

In the first snippet, the underlying iterator technology of the std::string class sets the end iterator (which is not reached in the short form for loop) to the NUL terminator. This behaviour is consistent with s.size().