Непонятны разные функции библиотеки cctype

#include <iostream>
#include <string>
#include <cctype>
 
void strcount(const std::string & str);
int main()
{
    using std::cout;
    using std::cin;
    using std::endl;
    using std::string;
    string input;
    cout << "Enter a line:\n";
    getline(cin, input);
    while(input != "")
    {
        strcount(input);
        cout << "Enter next line (empty line to quit): \n";
        getline(cin, input);
    }
    cout << "Bye\n";
    return 0;
}
void strcount(const std::string & str)
{
    using std::cout;
    static int total = 0;
    /*int blank = 0;
    for (int i = 0; i < str.size(); i++)                
        if (std::isblank(str[i]))
            blank++;
    int characters = str.size() - blank;*/
    //error: no matching function for call to 'isblank(const value_type&)'|
    //note: candidate: template<class _CharT> bool std::isblank(_CharT, const std::locale&)|
    //note:   template argument deduction/substitution failed:|
    //note:   candidate expects 2 arguments, 1 provided|
    int characters = 0;
    for(int i = 0; i < str.size(); i++)
        if (isgraph(str[i]))
            characters++;*/
    total += characters;
    cout << "\"" << str << "\" contains ";
    cout << characters << " characters.\n";
    cout << total << " characters total.\n";
}

#include <iostream>
#include <string>
#include <cctype>
 
void strcount(const std::string & str);
int main()
{
    using std::cout;
    using std::cin;
    using std::endl;
    using std::string;
    string input;
    cout << "Enter a line:\n";
    getline(cin, input);
    while(input != "")
    {
        strcount(input);
        cout << "Enter next line (empty line to quit): \n";
        getline(cin, input);
    }
    cout << "Bye\n";
    return 0;
}
void strcount(const std::string & str)
{
    using std::cout;
    static int total = 0;
    int blank = 0;
    for (int i = 0; i < str.size(); i++)
        if (isblank(str[i]))
            blank++;
    int characters = str.size() - blank;
    total += characters;
    cout << "\"" << str << "\" contains ";
    cout << characters << " characters.\n";
    cout << total << " characters total.\n";
}