错误：无法绑定 'std::ostream {aka std::basic_ostream<char> }'左值为'std::basic_ostream<char> &&'</char></char>

Question

So, I have recently approched OOP in c++ through university and I found myself with a few problems. I gave a shot at overloading the ostream operator << and found myself with some problems to solve. First was that doing the overloading as ostream& operator<<(ostream& outs, const Test&); carries a problem described as \src\Test.h:15:48: error: 'std::ostream& test::Test::operator<<(std::ostream&, const test::Test&)' must take exactly one argument ostream& operator<<(ostream& outs, const Test&); , so, just like I did with the operator == removed the second argument. But once i Try to build the following code i get the error: \src\main.cpp:9:10: error: cannot bind 'std::ostream {aka std::basic_ostream<char>}' lvalue to 'std::basic_ostream<char>&&' cout << t; . I read this error but can't comprhend it, what should I do and what is the mistake I'm doing?

Test.h

#include <iostream>
#include <cstring>
using namespace std;
#ifndef SRC_TEST_H_BECCIO
#define SRC_TEST_H_BECCIO

namespace test {

class Test {
private:
    string mStr;
public:
    Test(string str);
    string getString(){return this->mStr;};
    ostream& operator<<(ostream& outs);
};

} /* namespace test */

#endif /* SRC_TEST_H_BECCIO */

Test.cpp

#include "Test.h"

namespace test {

Test::Test(string str) {
    this->mStr=str;

}

ostream& Test::operator<<(ostream& outs){

    outs << this->getString()<<endl;
    return outs;
}

} /* namespace test */

main.cpp

#include <iostream>
#include "Test.h"
using namespace std;
using namespace test;

int main() {

    Test t("let's hope this goes well");
    cout << t;
    return 0;
}

Answer 1

It looks like the order of the arguments is backwards. See https://learn.microsoft.com/en-us/cpp/standard-library/overloading-the-output-operator-for-your-own-classes . Try this declaration, and a similar implementation:

friend ostream& operator<<(ostream& os, Test t);