Copy null terminated char array to std::string respecting buffer length

Question

Maybe it's just the lack of coffee, but I'm trying to create a std::string from a null-terminated char array with a known maximum length and I don't know, how to do it.

auto s = std::string(buffer, sizeof(buffer));

.. was my favorite candidate but since C++ strings are not null-terminated this command will copy sizeof(buffer) bytes regardless of any contained '\0'.

auto s = std::string(buffer);

.. copies from buffer until \0 is found. This is almost what I want but I can't trust the receive buffer so I'd like to provide a maximum length.

Of course, I can now integrate strnlen() like this:

auto s = std::string(buffer, strnlen(buffer, sizeof(buffer)));

But that seems dirty - it traverses the buffer twice and I have to deal with C-artifacts like string.h and strnlen() (and it's ugly).

How would I do this in modern C++?

Answer 1

Something like this could work in a single pass..

auto eos = false;
std::string s;
std::copy_if(buffer, buffer + sizeof(buffer), std::back_inserter(s),
  [&eos](auto v) {
    if (!eos) {
      if (v) {
        return true;
      }
      eos = true;
    }
    return false;
  });

Answer 2

const char* end = std::find(buffer, buffer + sizeof(buffer), '\0');
std::string s(buffer, end);