编译练习时std_lib_facilities.h C++错误

Question

我试图在Bjarne的“编程原理和实践使用C++”一书中为一个练习编写一个程序，这个程序应该是一个名为“公牛和奶牛”的小游戏，用户试图猜出一个四位数的数字。这是我到目前为止掌握的代码：

#include "../Library/std_lib_facilities.h"

class string_error{};

/*
 * Method to determine if an integer is
 * in a vector
 */
bool contains(vector<int> v,int k ){

}

int string_to_int(string s){
    if(s == "0") return 0;
    else if(s == "1")return 1;
    else if(s == "2")return 2;
    else if(s == "3")return 3;
    else if(s == "4")return 4;
    else if(s == "5")return 5;
    else if(s == "6")return 6;
    else if(s == "7")return 7;
    else if(s == "8")return 8;
    else if(s == "9")return 9;
    else throw string_error();
}

int main(){

    /*
     * There is an int vector with the numbers
     * of the answer in it
     *
     * There is also an int vector with the numbers
     * of the user's guess
     *
     * User inputs a four digit integer that is read as
     * a string called str_guess
     *
     * for each digit in the guess string the digit is
     * converted to an integer and added to the guess vector
     *
     * The guess vector is then run through for each digit in the vector
     * each digit is checked against the answer at the same index
     * if the digit in the answer at that index number is not the same as the
     * digit in the guess vector then the digit is checked if the answer
     * vector contains it at all
     *
     * for each number that is correct for both the value and position
     * 1 is added to the bull value
     * for each number that is within the answer value but not in the correct position
     * 1 is added to the cow value
     *
     * The bull and cow values are displayed after the user enters their guess
     *
     * The user is prompted for a guess until their guess returns 4 bulls
     */

    vector<int> answer;
    answer.push_back(7);
    answer.push_back(9);
    answer.push_back(2);
    answer.push_back(4);

    string str_guess = "";
    cout << "Enter a four digit integer as a guess";
    cin >> str_guess;
    vector<int> guess;
    for(int i = 0; i < 4; i++){
        int guess_digit = string_to_int(str_guess[i]);
        guess.push_back(guess_digit);
    }
    cout << "Length of guess vector: " + guess.size();



}

正如您所看到的，我使用的是Mr.Stroustrup先生的头文件std_lib_facilities.h(这里)，不幸的是，每当我试图编译我的程序时，我都会得到以下错误：

In file included from ../Bulls_and_Cows.cpp:13:
../../Library/std_lib_facilities.h:106:38: error: no matching constructor for initialization of 'std::string' (aka 'basic_string<char, char_traits<char>, allocator<char> >')
        template<class S> String(S s) :std::string(s) {}

我在mac上使用eclipse和mac os gcc编译器。如果你能为我提供任何帮助，我将不胜感激。谢谢

Answer 1

函数string_to_int接收一个字符串，并传递一个char。

int guess_digit = string_to_int(str_guess[i]);
//                                       ^^^ access a position of the string that is a char