Why won't my C++ code compile, getting undefined reference error

Question

For my class assignment, we had to make a C++ program using a class and then compile it. These are the following.

Snake.h

#ifndef SNAKE_H
#define SNAKE_H

#include <iostream>
using namespace std;

// We need to include string since we need to access it
#include <string>
using std::string;
// Our declaration of our class
class Snake
{
public:
    // These are our properties
    string color;
    double length;
    bool venomous;

    // Our two constructors, this is basically saying the snake is able to create these datatypes.
    // It can either have a default data used or inputted data when called.
    Snake()
    {
    }
    // This one has the parameters
    Snake(string color, double length, bool venomous)
    {
    }

    // Our functions that we are declaring so we can use them in snake.cpp
    // These aren't declared here because we don't have any data yet that they can use
    // We also are just telling the code that they are here and that they may or
    // may not be called at some point

    void display();
    void bite();
};

#endif

Snake.cpp

#include <iostream>
#include "Snake.h"

// These creates our data from the header file.
// Snake is seen below with the default data and then Snake with the parameters can be seen.
Snake::Snake()
{
    color = "Red";
    length = 12.5;
    venomous = false;
}

Snake::Snake(string newColor, double newLength, bool newVenomous)
{
    color = newColor;
    length = newLength;
    venomous = newVenomous;
}

// These initalize these functions so that they can be used when we do our dot callback in our main.
void Snake::bite()
{
    cout << "This snake bites because he is hungry";
}

void Snake::display()
{
    cout << "The color of the snake is: " << color;
    cout << "The length of the snake is: " << length;
    cout << "Is the snake venomous: " << venomous;
}

main.cpp

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

int main()
{
    // We create our first snake
    Snake snake1;
    // Now we need to call method that our object contains
    snake1.display();
    snake1.bite();

    // UI is user input
    bool UIVenomous;
    string UIColor, isVenomous;
    double UILength;

    cout << "What color is the snake?" << endl;
    cin >> UIColor;
    cout << "How long is the snake? " << endl;
    cin >> UILength;
    cout << "Is the snake venomous? (y/n) " << endl;
    cin >> isVenomous;
    if (isVenomous == "y")
    {
        UIVenomous = true;
    }
    else if (isVenomous == "n")
    {
        UIVenomous = false;
    }

    // We now call our class and set our object with the variables from above
    Snake snake2(UIColor, UILength, UIVenomous);
    // We need to now call our methods that our object has
    snake2.display();
    snake2.bite();
}

I am using VSCode and when I try to run build task it gives me this error

C:\Users\viens\AppData\Local\Temp\cclzLMka.o: In function `main':
c:/Users/viens/OneDrive/Documents/SchoolWork/Lab3/main.cpp:10: undefined reference to `Snake::display()'
c:/Users/viens/OneDrive/Documents/SchoolWork/Lab3/main.cpp:11: undefined reference to `Snake::bite()'
c:/Users/viens/OneDrive/Documents/SchoolWork/Lab3/main.cpp:36: undefined reference to `Snake::display()'
c:/Users/viens/OneDrive/Documents/SchoolWork/Lab3/main.cpp:37: undefined reference to `Snake::bite()'
collect2.exe: error: ld returned 1 exit status
The terminal process terminated with exit code: 1

Answer 1

If there's an undefined reference error, usually it's because the .o file (which gets created from the .cpp file) doesn't exist and your compiler/build system is not able to link it.

You can use this in CLI: g++ main.cpp other.cpp etc.cpp

Answer 2

It compiled regularly after I removed the bodies of constructors in the header file.

/* Snake.h
*/
Snake();
Snake(string color, double length, bool venomous);