How do I replace data of some range of std::vector

std::vector<char> v;
v.push_back('a');
v.push_back('b');
v.push_back('c');
v.push_back('d');
v.push_back('e');
v.push_back('f');

char c[3] = { 'z', 'x', 'y' };

// Want to make abzxyf
//v.insert(v.begin() + 2, c, c + 3); // it doesn't work as I wanted.

// Yes it works. but if c is more bigger, it will be crash.
std::copy(c, c + 3, v.begin() + 2);

v.clear();
v.push_back('a');
v.push_back('b');
v.push_back('c');
v.push_back('d');
v.push_back('e');
v.push_back('f');

// If vector needs more memory, I'd let him grow automactically
// So I tried this.(expected abcdezxy)
// But it's result is abcdezxyf. f is still remain.
std::copy(c, c + 3, std::inserter(v, v.begin() + 5));

What algorithm or method should I use?