C++ Linking to separate .cpp file says "multiple definitions" - c++

Question

I'm very new to C++ and could use some help. I'm trying to link a file my_help_fxns.cpp to my main.cpp file so i can use those functions in main.cpp, but when i try linking I get the following error for each function in my_help_fxns:
C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\Geoff\AppData\Local\Temp\ccaPL79E.o:data_vars_class.cpp:(.text+0x0): multiple definition of `my_help_fxns::print_vector_items_int_type(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<int, std::allocator<int> >)'; C:\Users\Geoff\AppData\Local\Temp\cc0mRP1w.o:main.cpp:(.text+0x0): first defined here
So it says I'm defining twice, but I don't know how to get around this. I have a class called data_vars_class. i include my_help_fxns at the top of data_vars_class.cpp, and use the helper fxns successfully in methods for that class. An instance of the class is created at the top of main.cpp. however if i try to use the helper functions in main() in main.cpp, without declaring "my_help_fxns.cpp" at the top of main.cpp, it says functions arent found, and if i do declare it at the top of main.cpp, i get the duplication error its been declared twice. How can I fix this, thanks!
this is the structure of my project
main.cpp ==>
#include "data_vars_class.hpp"
#include <iostream>
#include <chrono>
#include "my_help_fxns.cpp" <--- including here gives duplication error, but if i dont, its functions not found error
DataVars dataVars;
int main () {
my_help_fxns::pause_program();
return 0;
}
data_vars_class.hpp ==>
#include <string>
#include <vector>
#include <unordered_map>
#include <unordered_set>
class DataVars
{
private:
...
public:
...
}
data_vars_class.cpp ==>
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <array>
#include "data_vars_class.hpp"
#include "my_help_fxns.cpp"
...i can use my_help_fxns here with no problem, as an instance of this class is created before main() in main.cpp
my_help_fxns.cpp ==>
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <vector>
#include <algorithm>
#include <map>
using namespace std;
namespace my_help_fxns
{
void pause_program() {
std::string dummy;
std::cout << "Enter to continue..." << std::endl;
std::getline(std::cin, dummy);
}
}
And here is the build command for the file in Geany:
g++ main.cpp data_vars_class.cpp -o a.out
Thanks for your help!

Answer 1

Don't include the my_help_fxns.cpp into the other CPP files since that will effectively define those functions in all the CPP files. This violates the one definition rule.
Instead
create a header file that declares (but not defines) those functions
include that header file in all the CPP files
add my_help_fxns.cpp to the compilation command line

Answer 2

Make changes to your files as described:
main.cpp
#include "data_vars_class.hpp"
#include <iostream>
#include <chrono>
#include "my_help_fxns.hpp" // change file extension from cpp -> hpp
DataVars dataVars;
int main () {
my_help_fxns::pause_program();
return 0;
}
data_vars_class
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <array>
#include "data_vars_class.hpp"
// #include "my_help_fxns.cpp" --> Not required here
And then you may simply run:
g++ -o a.out main.cpp; ./a.out
Gives here:
Enter to continue...
sdfsdfsdfsd // --- INPUT