c++ - Error in including a Global Vector when used in multiple files - 


// main.cpp #include <iostream> #include "common.h" #include "second.cpp" #include <vector>  int main(){   global = 10;   ip.push_back("testtest");   std::cout << global << std::endl;   testclass t;   t.print(); }  //common.h #ifndef global_h #define global_h #include <vector>  #include <string> extern int global; extern std::vector<std::string> ip ;  #endif  // second.cpp  #include <iostream> #include "common.h"  int global;  class testclass{    public:     void print();}; void testclass::print(){   global++;   std::cout << "global: "<<global << std::endl;   std::cout << "ip string: "<<ip[0] << std::endl; }  // console error ubuntu:deleteme$ g++ main.cpp /tmp/ccojpyrl.o: in function `testclass::print()': main.cpp:(.text+0x55): undefined reference `ip' /tmp/ccojpyrl.o: in function `main': main.cpp:(.text+0xdd): undefined reference `ip' collect2: error: ld returned 1 exit status

the above works when using int global variable. when added vector ip common.h getting showed error.

this seems elemental thing couldn't answer.

thanks in advance :)

you didn't define std::vector<std::string>. extern declard it's global defined in place. should add definition under int global in second.cpp

// second.cpp  #include <iostream> #include "common.h"  int global; std::vector<std::string> ip;  class testclass{

as aside, shouldn't use globals.


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