通过运算符重载的字符串连接

Question

QUESTION

Write a C++ program to overload '+' operator to concatenate two strings.

This program is done on my OOP book of Robert Lafore fourth edition Object Oriented programming but seems to not be able to convert char to string. The program is well written and fulfills the requirement but the one error it gives makes it hard to understand. I cant seem to find the problem in it.

error it gives is that character cannot be converted to string.

#include <iostream>

using namespace std;#include <string.h>

#include <stdlib.h>

class String //user-defined string type
{
    private:
        enum {
            SZ = 80
        }; //size of String objects
    char str[SZ]; //holds a string

    public:
        String() //constructor, no args
    {
        strcpy(str, "");
    }
    String(char s[]) //constructor, one arg
    {
        strcpy(str, s);
    }
    void display() const //display the String
    {
        cout << str;
    }
    String operator + (String ss) const //add Strings
    {
        String temp;

        if (strlen(str) + strlen(ss.str) < SZ) {
            strcpy(temp.str, str); //copy this string to temp
            strcat(temp.str, ss.str); //add the argument string
        } else {
            cout << “\nString overflow”;
            exit(1);
        }
        return temp; //return temp String
    }
};

////////////////////////////////MAIN////////////////////////////////

int main() {
    String s1 = “\nMerry Christmas!“; //uses constructor 2
    String s2 = “Happy new year!”; //uses constructor 2
    String s3; //uses constructor 1

    s1.display(); //display strings
    s2.display();
    s3.display();

    s3 = s1 + s2; //add s2 to s1,

    //assign to s3
    s3.display();
    cout << endl;
    return 0;
}

Answer 1

Firstly, this “ / ” is not " , so the C++ compiler doesn't get that.

Second, a string literal is a const char[] , which decays into a const char* , so it won't call the char[] constructor.

The Fix:

String(const char* s) //takes a string literal
{
    strcpy(str, s);
}

Be sure to replace your quotes with ASCII quotes ( " ).