static variable link error [duplicate]

Question

I'm writing C++ code on a mac. Why do I get this error when compiling?:

Undefined symbols for architecture i386: "Log::theString", referenced from: Log::method(std::string) in libTest.a(Log.o) ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation)

Not sure if my code is wrong or I have to add additional flags to Xcode. My current XCode configurations are the default ones for a 'static library' project.

My code:

Log.h------------

#include <iostream> #include <string>  using namespace std;  class Log{ public:     static void method(string arg); private:     static string theString ; }; 

Log.cpp ----

#include "Log.h" #include <ostream>  void Log::method(string arg){     theString = "hola";     cout   << theString << endl;  } 

I'm calling the 'method' from a test code, in this way: 'Log::method("asd"):'

thanks for your help.

Answer 1

You must define the statics in the cpp file.

Log.cpp

#include "Log.h" #include <ostream>  string Log::theString;  // <---- define static here  void Log::method(string arg){     theString = "hola";     cout   << theString << endl;  } 

You should also remove using namespace std; from the header. Get into the habit while you still can. This will pollute the global namespace with std wherever you include the header.

Answer 2

You declared static string theString;, but haven't defined it.

Include

string Log::theString; 

to your cpp file