C++ External Class Implementation Not Working - c++

Question

I am trying to implement my own 'User' class from an external C++ file.
Therefore, I created a User.h, User.cpp and main.cpp file which are all in the same directory. Here you can see the source code of each file:
./User.h
#include <string>
class User {
public:
User(std::string username, std::string password);
std::string getPassword();
std::string username;
private:
std::string password;
};
./User.cpp
#include "User.h"
User::User(std::string username, std::string password) {
this -> username = username;
this -> password = password;
}
std::string User::getPassword() {
return password;
}
./main.cpp
#include <iostream>
#include "User.h"
int main() {
User eve("Eve3033", "Pass1234");
std::cout << eve.getPassword();
return 0;
}
The g++ compiler error:
undefined reference to `User::User(std::\__cxx11::basic_string\<char, std::char_traits\<char\>, std::allocator\<char\> \>, std::\__cxx11::basic_string\<char, std::char_traits\<char\>, std::allocator\<char\> \>)'
C:\\Users\\wise-\\AppData\\Local\\Temp\\ccQgLvm9.o:main.cpp:(.text+0xb8): undefined reference to `User::getPassword[abi:cxx11]()' collect2.exe: error: ld returned 1 exit status
I tried to remove the std::string User::getPassword() method, which didn't result in any compiling errors. The construction of the User eve("Eve3033", "Pass1234") instance was also successfull and I was able to access the public std::string username attribute.
However, when I tried to implement the std::string User::getPassword() method to also access the private std:string password attribute, g++ returned the same error.
I searched for the error online and found the following links:
Undefined reference to Class::Method()
Undefined Reference to Class::Function() in C++
How to fix undefined reference in C++
I hope you have any ideas on that problem :)

Answer 1

Your error must be due to a syntax error or missing file in your command. Compiling this code in VS works just fine, and has the expected output. Make sure you have: g++ main.cpp user.cpp
If you need more context and examples, see here.