c++ - Multiple definition of a function error, even when using #if guard clauses -

i creating simple util.h file contain aplusb(int, int) function c++ project. cannot compile , error message multiple definition of `aplusb(int, int)'. please me correct error or give me hints?

i attach here project detail reference.

file util.h

#ifndef util_h_ #define util_h_  int aplusb(int a, int b) {     return + b; }  #endif /* util_h_ */ 

file classa.h

#ifndef classa_h_ #define classa_h_  class classa { public:     classa();     virtual ~classa(); private:     int sum; };  #endif /* classa_h_ */ 

file classa.cpp

#include "classa.h" #include "util.h"  classa::classa() {     // todo auto-generated constructor stub     sum = aplusb(3,5);  }  classa::~classa() {     // todo auto-generated destructor stub } 

file classb.h

#ifndef classb_h_ #define classb_h_  class classb { public:     classb();     virtual ~classb(); private:     int sum; };  #endif /* classb_h_ */ 

file classb.cpp

#include "classb.h" #include "util.h"  classb::classb() {     // todo auto-generated constructor stub     sum = aplusb(5,6); }  classb::~classb() {     // todo auto-generated destructor stub } 

compile error message

classb.o: in function `aplusb(int, int)': /home/vtvan/desktop/workspace/commonfunc/util.h:11: multiple definition of `aplusb(int, int)' classa.o:/home/vtvan/desktop/workspace/commonfunc/util.h:11: first defined here collect2: error: ld returned 1 exit status make: *** [commonfunc] error 1 

first variant - use inline specifier

#ifndef util_h_ #define util_h_  inline int aplusb(int a, int b) {     return + b; }  #endif /* util_h_ */ 

second variant - write definition in .cpp file.