C String assigning values in explicit constructor in C++?

Question

I have a class BankAccount with two string members - name and num. What I want is to assign values to these objects when I create them (when the constructor is called). However the compiler says No instance of constructor matches the argument list when I try to create an object. I would like to ask why is that?

// hwk-2.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include "pch.h"
#include <iostream>
#include <string>
#include <stdio.h>
using namespace std;
class BankAccout {
    char name[23];
    char num[15];
    double sum;
public:
    BankAccout(char *nm, char *nr, double s) {
        strcpy(name,nm);
        strcpy(num, nr);
        sum = s;
    }


};
int main()
{
    BankAccout k("Peter", "0403940940", 34.21);

}

Use const char* instead of char* in the constructor parameters. String literals are const char[] values, which decay to const char*, not to char*. Though, you really should be using std::string instead of char[] arrays to begin with. This is C++, not C, afterall — Remy Lebeau
– Remy Lebeau, Commented Oct 9, 2018 at 20:03
Why does getName() return a std::string but you aren't using one anywhere else? Everywhere you have a c-string you should be using a std::string. — NathanOliver
– NathanOliver, Commented Oct 9, 2018 at 20:05
why the downvote people? Its a great question. Its clear, it says what the issue is, it includes the complete source code needed to reproduce. I wish all rep == 1 questions were like this — pm100
– pm100, Commented Oct 9, 2018 at 20:09

pm100 · Accepted Answer · 2018-10-09 20:45:43Z

1

as a coffee break exercise here is more idiomatic version

#include "pch.h"
#include <iostream>
#include <string>

class BankAccount {
    std::string name_;
    std::string num_;
    double sum_;
public:
    BankAccount(std::string name, std::string num, double sum) {
        name_ = name;
        num_ = num;
        sum_ = sum;
    }
};

int main()
{
    BankAccount k("Peter", "0403940940", 34.21);
}

answered Oct 9, 2018 at 20:45

pm100

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2 Comments

juanchopanza Over a year ago

It would be even more idiomatic to use constructor initialization lists and move the string constructor parameters into the data members.

David Over a year ago

I agree this solution is nice. But it does not answer the question of the OP: Why does the compiler not find a constructor that matches his actual parameters. Which I think is a quite interesting question for beginners. But anyway, there is also much to learn from your idiomatic version, that is true as well.

David · Accepted Answer · 2018-10-09 21:39:17Z

1

The signature of the constructor does not match. This one will match:

BankAccount(const char *nm, const char *nr, double s);

EDIT:

The reason is the way you are calling the constructor in the main function. You are giving literal strings as parameters. These literals are const, you cannot change them at runtime. Thus you will pass pointers to const char*.

This is very obvious if you look at this opposing example. This is a way that would be compatible with the old signature BankAccout(char *nm, char *nr, double s);.

int main(int argc, char* argv[])
{
    char name[] = "hello";
    char number[] = "1234";

    std::cout << "name before: " << name << std::endl;

    BankAccount k(name, number, 8.5);

    // name and number are not const,
    // you can change them :
    name[2] = 'x';
    name[3] = 'x';

    std::cout << "name after: " << name << std::endl;

    return 0;
}

edited Oct 9, 2018 at 21:39

answered Oct 9, 2018 at 20:07

David

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2 Comments

pm100 Over a year ago

but dont do that anyway, use std::string everywhere

NathanOliver Over a year ago

It would helpful to the OP and future readers if you could explain why this change is needed.

Kuba hasn't forgotten Monica · Accepted Answer · 2018-10-09 23:17:35Z

0

An even simpler version, if you don’t need to have additional functionality in the class: just use a struct.

#include <string>

struct BankAccount {
  std::string name;
  std::string number;
  double balance;
};

int main() {
  BankAccount account{"Joy", "44", 43.};
}

answered Oct 9, 2018 at 23:17

Kuba hasn't forgotten Monica

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