Constructors That Use Part of a C-Style String

Constructors that use part of a C-style string let you initialize a string object from part of a C-style string; more generally, they let you initialize a charT specialization from part of an array of charT values:

basic_string(const charT* s, size_type n, const Allocator& a = Allocator());

This constructor copies to the constructed object a total of n characters from the array pointed to by s. Note that it doesn’t stop copying if s has fewer characters than n. If n exceeds the length of s, the constructor interprets the contents of memory following the string as if they held data of type charT.

This constructor requires that s is not a null pointer and that n < npos. (Recall that npos is a static class constant equal to the maximum possible number of elements in a string.) If n equals npos, the constructor throws an out_of_range exception. (Because n is of type size_type and npos is the maximum size_type value, n cannot be greater than npos.) Otherwise, the following relationships hold after the constructor is called:

• The data() method returns a pointer to the first element of a copy of the array s.

• The size() method returns n.

• The capacity() method returns a value at least as large as size().