Unable to overload stream extraction operator (>>) in C++ - c++

Question

I'm currently trying to understand the basic concepts of operator overloading in C++. Therefore, I created a class wheel that is able to read from a stream by overloading the stream extraction operator >>.
wheel.h
#ifndef WHEEL_H
#define WHEEL_H
#include <cassert>
#include <ostream>
#include <string>
class wheel final {
float rimDiameter;
int productionYear;
std::string velocityIndex = "N/A";
std::string manufacturer = "N/A";
public:
wheel() = default;
wheel( float rimDiameter,
int productionYear,
std::string velocityIndex,
std::string manufacturer
) : rimDiameter{rimDiameter},
productionYear{productionYear},
velocityIndex{velocityIndex},
manufacturer{manufacturer}
{}
~wheel() = default;
friend
auto operator<<(std::ostream &os, const wheel &self) -> std::ostream &;
friend
auto operator>>(std::istream &is, wheel &self) -> std::istream &;
};
#endif
wheel.cpp
#include "wheel.h"
auto operator<<(std::ostream &os, const wheel &self) -> std::ostream & {
return os << " WHEEL" << std::endl
<< " =============================" << std::endl
<< " Rim Diameter: " << self.rimDiameter << "\"" << std::endl
<< " Year of Production: " << self.productionYear << std::endl
<< " Velocity Index: " << self.velocityIndex << std::endl
<< " Manufacutrer: " << self.manufacturer << std::endl;
}
auto operator>>(std::istream &is, wheel &self) -> std::istream & {
char c[3];
is >>
self.rimDiameter >> c[0] >>
self.productionYear >> c[1] >>
self.velocityIndex >> c[2] >>
self.manufacturer;
assert(c[0] == ';' && c[1] == ';' && c[2] == ';');
return is;
}
main.cpp
#include <iostream>
#include "wheel.h"
int main(void) {
wheel w;
std::cin >> w;
std::cout << w;
return 0;
}
To me, it all looks fine, but somehow I keep getting an error telling me that there is no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'float'):
$ make
g++-7 -g -std=c++17 -Wall -Wextra -Wconversion -Wpedantic -c main.cpp
g++-7 -g -std=c++17 -Wall -Wextra -Wconversion -Wpedantic -c wheel.cpp
wheel.cpp: In function 'std::istream& operator>>(std::istream&, wheel&)':
wheel.cpp:16:8: error: no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'float')
is >>
~~~^~
self.rimDiameter >> c[0] >>
~~~~~~~~~~~~~~~~
wheel.cpp:13:6: note: candidate: std::istream& operator>>(std::istream&, wheel&)
auto operator>>(std::istream &is, wheel &self) -> std::istream & {
^~~~~~~~
wheel.cpp:13:6: note: no known conversion for argument 2 from 'float' to 'wheel&'
In file included from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/string:53:0,
from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/bits/locale_classes.h:40,
from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/bits/ios_base.h:41,
from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/ios:42,
from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/ostream:38,
from wheel.h:5,
from wheel.cpp:1:
/usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/bits/basic_string.tcc:1465:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
operator>>(basic_istream<_CharT, _Traits>& __in,
^~~~~~~~
/usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/bits/basic_string.tcc:1465:5: note: template argument deduction/substitution failed:
wheel.cpp:17:14: note: mismatched types 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' and 'float'
self.rimDiameter >> c[0] >>
^~~~~~~~~~~
make: *** [wheel.o] Error 1
What am I missing here?

Answer 1

You need to include iostream for input and output like this #include <iostream> and you'll avoid the error.
When outputting, it's the class over which the << operators are defined you always use ostream, but you forgot the case of inputting for >>.
#ifndef WHEEL_H
#define WHEEL_H
#include <cassert>
#include <iostream>
#include <string>
class wheel final {
float rimDiameter;
int productionYear;
std::string velocityIndex = "N/A";
std::string manufacturer = "N/A";
public:
wheel() = default;
wheel( float rimDiameter,
int productionYear,
std::string velocityIndex,
std::string manufacturer
) : rimDiameter{rimDiameter},
productionYear{productionYear},
velocityIndex{velocityIndex},
manufacturer{manufacturer}
{}
~wheel() = default;
friend
auto operator<<(std::ostream &os, const wheel &self) -> std::ostream &;
friend
auto operator >> (std::istream &is, wheel &self) -> std::istream &;
};
#endif /* wheel_hpp */

Answer 2

As #Ext3h pointed out, I am missing the respective include for istream.
Adding #include <istream> to wheel.h resolves the problem.
Thank you very much for you help, would have taken me forever to figure out the issue!