c++ compiling error for reading object from file - c++

Question

I saved objects to file and while reading them back i want to write it content to output stream. I did add operator overloading for it friend std::ostream& operator<<(std::ostream& out, T& c) but how to do it in correct way?
#include <iostream>
#include <fstream>
class MySpecificClass {
std::string data;
unsigned int x;
unsigned int y;
unsigned int z;
public:
MySpecificClass(): data(""), x(0), y(0), z(0) {}
MySpecificClass(std::string s, unsigned int xx, unsigned int yy, unsigned zz) : data(s), x(xx), y(yy), z(zz) {}
std::string Print() {
std::string s = "data: " + data + "\tx=" + std::to_string(x) + ",\ty=" + std::to_string(y) + ",\tz=" + std::to_string(z);
return s;
}
};
template <class T>
class IFileClass {
public:
IFileClass(std::string f) : fileName(f) {}
virtual void save(T& c) = 0;
virtual void read(T& c) = 0;
protected:
std::string fileName;
std::ofstream fout;
std::ifstream fin;
};
template <class T>
class FileWithClass : public IFileClass<T> {
public:
FileWithClass(std::string fn) : IFileClass<T>(fn) {
std::cout << "FileWithClass constructor" << std::endl;
}
friend std::ostream& operator<<(std::ostream& out, T& c) {
out << c.Print();
return out;
}
void save(T& c) override {
if (this->fileName == "")
throw new std::runtime_error("path is empty");
this->fout.open(this->fileName, std::ofstream::app);
if (this->fout.is_open()) {
this->fout.write((char*)&c, sizeof(T));
this->fout.close();
std::cout << "saved" << std::endl;
} else {
std::cout << "File open error" << std::endl;
}
}
void read(T& c) override {
if (this->fileName == "")
throw new std::runtime_error("path is empty");
this->fin.open(this->fileName);
if (this->fin.is_open()) {
while (this->fin.read((char*)&c, sizeof(T))) {
std::cout << c << std::endl;
}
this->fin.close();
} else {
std::cout << "File open error" << std::endl;
}
}
};
int main() {
MySpecificClass msc = {"My text", 1, 2, 3};
FileWithClass<MySpecificClass> fsv = {"test.txt"};
fsv.save(msc);
fsv.read(msc);
}
In line std::cout << c << std::endl; I get a compile error:
main.cpp|71|error: no match for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'MySpecificClass')

Answer 1

Basically this, outside of your class definition:
std::ostream& operator<<(std::ostream& out, MySpecificClass& c) {
out << c.Print();
return out;
}
You don't need to add the friend function definition, because you are not using any private members in your operator<<. And if you were, you would actually need to declare it friend in MySpecificClass, and not your template, because your template class has no access to MySpecificClass private data.