c++ - Should I use both header files and cpp/source files? -

i have mammal.h file reads:

#ifndef mammal_h #define mammal_h  class mammal { public:     void speak(); };  #endif 

my cpp file looks like:

#include "stdafx.h" #include "mammal.h" #include <iostream>  void mammal::speak() {     using namespace std;      cout << "speaking"; } 

and use of code seen here:

#include "stdafx.h" #include "mammal.h"  int main() {     mammal *mammal = new mammal();      mammal->speak(); } 

however, could in header file:

#include "stdafx.h" #include <iostream>  #ifndef mammal_h #define mammal_h  class mammal { public:     void speak()     {         using namespace std;          cout << "speaking";     } };  #endif 

i haven't defined preference...but see both work. there advantages or disadvantages either of these approaches?

try calling code more 1 place -- , therefore #including header in more 1 source file -- , you'll see problem in second approach. linker doesn't if have more 1 definition of same function, if they're identical.