How to fix 'Invalid operands to binary expression' error in C++

Question

I'm trying to make a program which saves in an object, all names got from another object, for example I have class Cheltuieli which saves a char and I have class Repo which saves an array with chars from Cheltuieli

I've tried changing cout << *c; with cout << *c->getName(); and I only get 1 letter: p instead of ["pizza", "pizza"]

Mancare.hpp

#ifndef Mancare_hpp
#define Mancare_hpp

class Cheltuieli{
private:
    char* name;
public:
    Cheltuieli();
    Cheltuieli(char* n);
    ~Cheltuieli();
    void setName(char* n);
    char* getName();
};

#endif

Mancare.cpp

#include "Mancare.hpp"
#include <string.h>

Cheltuieli::Cheltuieli()
{
    this -> name = NULL;
}
Cheltuieli::Cheltuieli(char* n)
{
    this -> name = new char[strlen(n) + 1];
    strcpy(this -> name, n);
}

Cheltuieli::~Cheltuieli()
{
    if(this -> name != NULL)
    {
        delete[] this -> name;
        this -> name = NULL;
    }
}

void Cheltuieli::setName(char *n)
{
    if(this -> name)
        delete[] this -> name;
    this -> name = new char[strlen(n) + 1];
    strcpy(this -> name, n);
}

char *Cheltuieli::getName()
{
    return this -> name;
}

void Repo::addElement(Cheltuieli &c)
{
    this -> cheltuieli[this -> size] = c;
    this -> size++;
}

Cheltuieli* Repo::getAll()
{
    return this -> cheltuieli;
}

char* const ps = "pizza";
Cheltuieli a = Cheltuieli(ps);

Repo n = Repo();
n.addElement(a);
n.addElement(a);

Cheltuieli* c = n.getAll();
cout << *c;

I get the output: 0x100503b38 with error Invalid operands to binary expression ('std::__1::ostream' (aka 'basic_ostream') and 'Cheltuieli')

Thank you!

You need at least to show the `Cheltuieli` class. Read this: [ask] and this: [mcve] — Jabberwocky, Mar 28 '19 at 14:45
To print `Cheltuieli` to `cout` you have to define `operator<<` in `Cheltuieli` class. — Amadeusz, Mar 28 '19 at 14:48
@Amadeusz Not *in* the class, but there needs to be a global overload for `operator<<` taking an output stream and a `Cheltuieli` class as arguments. — Some programmer dude, Mar 28 '19 at 14:50
`*c->getName()` is equal to `*(c->getName())`, which is equal to `(c->getName())[0]`. — Some programmer dude, Mar 28 '19 at 14:51
And perhaps you should [get a couple of good books](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list/388282#388282) to read to understand why `cout << *c` won't work? — Some programmer dude, Mar 28 '19 at 14:52

Theodor Badea · Answer 1 · 2019-03-29T09:28:18.783

0

Try overloading << operator in Cheltuieli:

    friend ostream& operator<<(ostream& os, const Cheltuieli& x)
    {
        os << x.name;
        return os;
    }

edited Mar 29 '19 at 09:28

answered Mar 28 '19 at 15:33

Theodor Badea

465
2
9

1

No `friend` declaration and `Date`? – Ted Lyngmo Mar 28 '19 at 16:20
@TedLyngmo my bad, this is the example from Microsoft msdn. Date is Cheltuieli and yes, it is friend. – Theodor Badea Mar 29 '19 at 07:32
You can [edit](https://stackoverflow.com/posts/55401504/edit) the answer so it fits the question. – Ted Lyngmo Mar 29 '19 at 09:17
You need to make the friend declaration in the class and put the definition at global scope. – Ted Lyngmo Mar 29 '19 at 09:50
You can put them both in the class @TedLyngmo, but I guess it is a better practice to do as you said. – Theodor Badea Mar 29 '19 at 10:01
1

You are correct. I let my own preferences shine through. My bad. I will actually start doing them inline to remind myself of this in the future :-) – Ted Lyngmo Mar 29 '19 at 11:56

score 0 · Accepted Answer · answered Mar 28 '19 at 16:40

From what I can tell, the Cheltuieli class is implementing a very small subset of what's already done in the std::string class - but it's incomplete, so if you do:

Cheltuieli orig("something");
Cheltuieli cpy = orig;

both orig and cpy will have a name member pointing at the same address because of the default copy constructor. Read about The rule of three/five/zero.

Similarly, the Repo class seems to be implementing something close to a std::vector. I suggest that you don't start fiddling about with raw pointers but to use the standard classes for this. You could even make aliases for them:

using Cheltuieli = std::string;
using Repo = std::vector<Cheltuieli>;

Used like this:

Cheltuieli a = "pizza";
Repo n;
n.push_back(a);
n.push_back(a);

for(auto& cheltuieli : n) {
    std::cout << cheltuieli << "\n";
}

How to fix 'Invalid operands to binary expression' error in C++

2 Answers2