The situation and solution of Link1169 in C++

Link1169 appears, usually one or more functions are found in the compiled obj file, so that the link does not know which function to choose

1. Code Situation:
   File A:

   #include <iostream>
   
   #define cs int
   
   cs Mutiply(int a,int b) {
   	cs result = a * b;
   	return result;
   #include "flag.h"
   
   
   void Log(const char* message) {
   		std::cout << message << std::endl;
   }

   file B:

   #include <iostream>
   
   void Log(const char* message) {
       std::cout << message << std::endl;
   }

   file C:

   #include <iostream>
    
   
   void Log(const char* message); 
   
   
   int main() {
       Log("Hello world!");
       std::cin.get();
   }
   
   

   In the case of the above code, file B and file A have exactly the same Log() function, so when looking for links, I don’t know which one to choose.
   
    
2. Solution: Delete the Log() function in file B or file A