I'm going through Mr. Stroustrup's "A Tour of C " book. In section 9.3 String Views, the author gives the following example:

string cat(string_view sv1, string_view sv2)
{
    string res(sv1.length() sv2.length());
    char *p = &res[0];
    for (char c : sv1) // one way to copy
        *p   = c;
    copy(sv2.begin(),sv2.end(),p); // another way
    return res;
}

When I try to compile this function, I get following error as std::string class doesn't provide any constructor which takes a single int parameter.

error: no matching function for call to 'std::__cxx11::basic_string<char>::basic_string(std::basic_string_view<char>::size_type)'   11 |     string res(sv1.length() sv2.length());

I checked the Errata for 2nd printing of A Tour of C but there is no mention of this issue.

Is this a bug in the example provide or else I'm missing something else?

CodePudding user response：

Is this a bug in the example provide or else I'm missing something else?

Yes this is an erratum in the book as std::string doesn't have a constructor that has only one parameter of type int(or convertible to int).

Instead it has a constructor std::string::string(size_type, char) that can take a char as the second argument. In particular, from std::string:

fill (6)  string (size_t n, char c);

(6) fill constructor: Fills the string with n consecutive copies of character c.

Thus to resolve the erratum, we should pass a second argument as shown below:

string res(sv1.length() sv2.length(), '\0');