C++ Multiple definition of helper function - c++

Question

EDIT: Answered -- the issue was that because the functions had the same signature, despite them being in separate files, C++ saw both versions and got confused.
I have three classes: Table and Bed both inherit from Furniture.
Table and Bed each have a helper function GetLowerCase(std::string) defined in each class individually. When make is run (Makefile shown below), I get an error saying that GetLowerCase in Bed.cpp was first defined in Table.cpp
Makefile:
main: main.o Furniture.o Table.o Bed.o
g++ main.o Furniture.o Table.o Bed.o -o main
main.o: main.cpp
g++ -c main.cpp
Furniture.o: Furniture.cpp Furniture.h
g++ -c Furniture.cpp
Table.o: Furniture.cpp Table.cpp Table.h
g++ -c Table.cpp
Bed.o: Furniture.cpp Bed.cpp Bed.h
g++ -c Bed.cpp
clean:
rm *.o main
Table.cpp:
#include "Table.h"
#include <iostream>
#include <string>
std::string GetLowerCase(std::string str)
{
std::string out;
for (int i=0; i<str.length(); i++)
{
out[i] = tolower(str[i]);
}
return out;
}
Table::Table(const std::string n, std::string wt) : Furniture(n)
{
wood_type = GetLowerCase(wt);
if (wood_type != "pine" && wood_type != "oak")
{
std::cerr << "Wood type must be OAK or PINE.";
}
}
void Table::Print()
{
Furniture::Print();
std::cout << "Wood Type: " << wood_type << std::endl;
}
Bed.cpp:
#include "Bed.h"
#include <iostream>
#include <string>
std::string GetLowerCase(std::string str)
{
std::string out;
for (int i=0; i<str.length(); i++)
{
out[i] = tolower(str[i]);
}
return out;
}
Bed::Bed(const std::string n, std::string sz) : Furniture(n)
{
size = GetLowerCase(sz);
if (size != "twin" && size != "full" && size != "queen" && size != "king")
{
std::cerr << "Bed size must be TWIN, FULL, QUEEN, or KING.";
}
}
void Bed::Print()
{
Furniture::Print();
std::cout << "Size: " << size << std::endl;
}
I would have thought that GetLowerCase would be entirely contained within the .cpp file it was defined in and wouldn't be "seen" by any other files.
It's not in any header or source files besides the two listed above. Very confused, and would love some help!

Answer 1

Either declare your function static or wrap it in an anonymous namespace:
namespace {
// duplicated names here.
}

Answer 2

Your options:
Move all your helper functions into a helper class (like CommomUtils) as static member functions. I recommend this way, it's more C++, and you can avoid duplicate code.
Declare your function as static. So its scope would be in file that defines it, rather than global.
Warp your function with namespace.
Defines your function only once, and in file you want to use it, use extern std::string GetLowerCase(std::string str) to declare it, then you can call it.