C++ 有输入到类

Question

I made 2 function : getdata, print for input/print variable in person class

    #include <iostream>
    #include <string>

    using namespace std;

    class person {
          public:
               char name[19];
               int born_year, married_year;
    };

    void getdata(char* name, int born_year,int married_year) {
         cout << "Enter Name!\n > ";
         cin.getline(name, 19);                         
         cout << "What's the Born Year?\n > ";
         cin >> born_year;
         cout << "What's the Married Year?\n > ";
         cin >> married_year;
    }

    void print(char* name, int born_year, int married_year) {
         cout << "Your Name : " << *name;
         cout << "\n Your Born Year : " << born_year;
         cout << "\n Your Married Year : " << married_year;
    }


    int main(void) {
        person p;
        int born_year, married_year;
        getdata(p.name, p.born_year, married_year);
        print(p.name, p.born_year, p.married_year);
        return 0;
    }

I'm trying to have input in a function outside the class

(class only have variables about person)

and print with with other function. How could I make this work?

Answer 1

Everything looks fine. Just you need to call 'function by reference' to directly change values of class variable. https://www.tutorialspoint.com/cplusplus/cpp_function_call_by_reference.htm

void getdata(char* name, int born_year,int married_year)

you can remove variables declared in main function and use p. before every parameter.

getdata(p.name, p.born_year, p.married_year);

Answer 2

Your problem is in the variable types to your getdata function. The integer parameters need to be pass-by-reference (either pointers or references, the latter being preferred). Right now you pass in a copy of the born_year and married_year values. When you get the input you save that into local variables; the passed parameters are never updated.

You want something like this:

void getdata(char* name, int &born_year,int &married_year)

With that tiny change (adding the two & characters) your code should work as you expect.

Answer 3

If you want passed variables to be changed inside a function you need to pass them by reference. To do that you need to make some changes in your function definition:

void getdata(char* &name, int &born_year, int &married_year) {
   //things you function does
}

Answer 4

#include <iostream>
#include <string>

using namespace std;

class person {
public:
    char name[19];
    int born_year, married_year;
};

void getdata(char* name, int &born_year, int &married_year) {
    cout << "Enter Name!\n > ";
    cin.getline(name, 19);
    cout << "What's the Born Year?\n > ";
    cin >> born_year;
    cout << "What's the Married Year?\n > ";
    cin >> married_year;
}

void print(char* name, int born_year, int married_year) {
    cout << "Your Name : " << name;
    cout << "\n Your Born Year : " << born_year;
    cout << "\n Your Married Year : " << married_year;
}


int main(void) {
    person p;
    getdata(p.name, p.born_year, p.married_year);
    print(p.name, p.born_year, p.married_year);
    return 0;
}

Answer 5

As others have mentioned your problem was that you were passing copies of the values in, not the variables themselves. Also you forgot to put the "p" on "married_year" in your main loop.

However, rather than passing in the separate values by reference, a much nicer idea is passing in a reference to the whole person:

int main(void) {
    person p;
    getdata(p);
    print(p);
    return 0;
}

Getdata and print would look like this:

void getdata(person &p) {
    cout << "Enter Name!\n > ";
    cin.getline(p.name, 19);                          
    cout << "What's the Born Year?\n > ";
    cin >> p.born_year;
    cout << "What's the Married Year?\n > ";
    cin >> p.married_year;
}

void print(const person &p) {
    cout << "Your Name : " << *(p.name);
    cout << "\n Your Born Year : " << p.born_year;
    cout << "\n Your Married Year : " << p.married_year;
}

It's a cleaner way to do it, and since you're not creating or passing as many variables around, there are less ways to make a mistake here. If you made the fields private however, you'd need to make the two functions "friend" of the class to access its members.