Error even duplicate characters

Question

For a school project, the class was asked to write a class Stringto simulate the STL class String.

I have all the code written, but it seems the linker is tied to one of my statements.

There are three files String.h, String.cppandtest2.cpp

Mine Makefilelooks like

CC=gcc
CXX=g++
CXXFLAGS+=-Wall -Wextra
LDLIBS+=-lstdc++

all:test2

test2:test2.o String.o
test2.o:test2.cpp String.h
String.o:String.cpp String.h

make outputs the following:

g++ -Wall -Wextra   -c -o test2.o test2.cpp
g++ -Wall -Wextra   -c -o String.o String.cpp
g++   test2.o String.o  -lstdc++ -o test2
ld: duplicate symbol operator==(String const&, char const*)in String.o and test2.o
collect2: ld returned 1 exit status
make: *** [test2] Error 1

This is odd since the only place I define operator ==is in String.h:

#ifndef MY_STRING_H
#define MY_STRING_H
#include <ostream>
#include <istream>

class String {
    //...
};

// ... operators ...

bool operator ==(const String& left, const char* right)
    { return left.compare_to(right)==0; }
bool operator ==(const char* left, const String& right)
    { return right.compare_to(left)==0; }
bool operator ==(const String& left, const String& right)
    { return left.compare_to(right)==0; }

// ... other comparison operators ...
#endif

test2.cpponly has an open method main:

#include "String.h"
using namespace std;

int main() {

}

So, if I define only operator ==(const String&, const char*)in one place, why does he say that I have a duplicate?

Answer 1

, String.cpp, test2.cpp.
.

// in String.h:
bool operator==(const String& left, const char* right);

// in String.cpp:
bool operator ==(const String& left, const char* right) {
    return left.compare_to(right)==0; 
}