c++ include header get failed

recently I've started learning c++. When I tried to write my header file, I got include error. Here is my code: First is the header file(header.h)

#pragma once void print(int); 

and then is its cpp file(header.cpp)

#include "header.h" #include <iostream> using namespace std; void print(int x){ cout << x << endl; } 

and finally my main cpp program(main.cpp)

#include <iostream> #include "./header.h" using namespace std; int main(){ int x = 123; print(x); } 

Here is the error, I can't figure out what it's saying orz

cd "/Users/yianchen/Desktop/cpp practice/" && g++ main.cpp -o main && "/Users/yianchen/Desktop/cpp practice/"main Undefined symbols for architecture x86_64: "print(int)", referenced from: _main in main-90c620.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

I have searched for some solution, when I use

#include "header.cpp" 

It works fine, but I see guys unrecommended using #include some_file.cpp

By the way, I use visual studio code and use code runner. Thanks!