How to make this code work with char instead of string?

Question

I am trying to complete a task, but I have to do it without using string. My goal is to read a text file, find lines containing the same CD name, but different actions (A or B) and then write the output in a different file. For example:

Input file:

10 B 01010112345 ABBA
15 A 02020213456 U2
16 A 03030314567 4you
17 B 02020213456 ABBA
20 B 04040415678 4you
127 B 04040415678 HipHop2014
1234 A 05050516789 ABBA

Output file:

20 03030314567 04040415678
1234 05050516789 01010112345

This is my code:

#include <iostream>
#include <cstring>
#include <fstream>
using namespace std;

const int SIZE = 250;
struct CD {
    int time;
    char action;
//    char person_code[12];
//    char cd[50];
    string person_code;
    string cd;
    bool removed = false;
};

int main(){
    fstream f("exchange.in");
    ofstream fout("exchange.out");
    CD m[SIZE];
    CD x;
    int it = 0, counter = 0;

    while(f>>x.time>>x.action>>x.person_code>>x.cd && it<SIZE){
        cout<<"Time: "<<x.time<<" Action: "<<x.action<<" Person code: "<<x.person_code<<" CD: "<<x.cd<<endl;
        m[it].time = x.time;
        m[it].action = x.action;
//        memcpy(&m[it].person_code, &x.person_code, sizeof(CD));
//        memcpy(&m[it].cd, &x.cd, sizeof(CD));
        m[it].person_code = x.person_code;
        m[it].cd = x.cd;
        it++;
    }
    for(int i=0; i<it; i++){
        for(int j=0; j<it; j++){
            if(!m[i].removed && !m[j].removed && m[i].cd == m[j].cd && m[i].action == 'A' && m[j].action == 'B'){
                int temp;
                if(m[i].time > m[j].time) {
                    temp = m[i].time;
                }
                else{
                    temp = m[j].time;
                }
                cout<<"Time: "<<temp<<" PC1: "<<m[i].person_code<<" PC2: "<<m[j].person_code<<endl;
                fout<<temp<<' '<<m[i].person_code<<' '<<m[j].person_code<<endl;
                counter++;
                m[i].removed = true;
                m[j].removed = true;
            }
        }
    }

    if(counter == 0) fout<<0<<"\n";

    f.close();
    fout.close();
}

As you can see, I've commented out the lines with char (person_code and cd). Right now the code is working with string (it outputs the same information as given above in my examples), but when I use char, the output file is blank.

What is a [mcve] demonstrating what is wrong? What do you get, in terms of output or errors during compilation? Please take the [tour] and read [ask] as general reference. — Ulrich Eckhardt, May 22 '21 at 13:06

score 1 · Answer 1 · answered May 22 '21 at 13:36

1

This code:

 m[i].cd == m[j].cd

Will check if the values have the same contents when cd is a std::string

Will check if the values have the same address when cd is an array. You're comparing pointers.

See How do I properly compare strings in C? if you are unsure of how to comapre C style strings.

answered May 22 '21 at 13:36

Drew Dormann

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Thank you! This was very useful! – Krabis May 22 '21 at 13:45

How to make this code work with char instead of string?

1 Answers1