How to convert a char array to a string?

Converting a C++ string to a char array is pretty straightorward using the c_str function of string and then doing strcpy. However, how to do the opposite?

I have a char array like: char arr[ ] = "This is a test"; to be converted back to:
string str = "This is a test.

The string class has a constructor that takes a NULL-terminated C-string:

char arr[ ] = "This is a test";

string str(arr);

//  You can also assign directly to a string.
str = "This is another string";

// or
str = arr;

Stack Overflow Q#8960087, score: 430