C ++ unresolved external character

Question

Hi iam begginer in C ++ I have a class with static methods and I cannot access them, this causes an error

1>------ Build started: Project: CPractice, Configuration: Debug Win32 ------ 1> Source.cpp 1>Source.obj : error LNK2001: unresolved external symbol "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > CPractice::name" ( ?name@CPractice @@ 0V?$basic_string@DU ?$char_traits@D @ std@ @ V?$allocator@D @ 2@ @ std@ @A) 1>c:\users\innersoft\documents\visual studio 2012\Projects\CPractice\Debug\CPractice.exe : fatal error LNK1120: 1 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== 

and here is my code

 #include <iostream> #include <stdio.h> #include <cstdlib> #include <string> using namespace std; class CPractice { public: static void setName(string s) { name = s; } static string getName() { return name; } private: static string name; }; int main() { CPractice::setName("Name"); cout << "\n" << CPractice::getName(); system("PAUSE"); return EXIT_SUCCESS; } 

Answer 1

 static string name; 

Since this is static , this line only declares name - you also need to define it. Just put this below your class definition:

 string CPractice::name; 

If you move your class to the appropriate header and implementation file, make sure you put this definition in the implementation file. It must be defined in only one translation unit.

Answer 2

I think you are trying to compile with gcc when you should compile with g++ . For more details, see What is the difference between g ++ and gcc? .

You also need to add string CPractice::name; below your class definition.

Answer 3

You just declared name in the class, static variables should be defined as outside the class:

 string CPractice::name ="hello" ; 

Answer 4

Since the name is a static data member, you should initialize it :) and not rely on the constructor associated with the default instance.

Add this after the class definitions (yep, I know that it is confusing since your member is private, but this is just initialization):

 string CPractice::name;