奇怪的链接器错误与静态std :: map [英] Weird linker error with static std::map

问题描述

为什么当我尝试在Visual Studio 2008中编译时会出现链接器错误

  #include< stdafx.h> ; 
 #include< iostream> 
 #include< map> 
 #include< string> 
 
 class MyClass 
 {
 public：
 MyClass（）{}; 
 virtual〜MyClass（）{}; 
 
 static std :: string niceString（std :: map< int，int> mappp）{_myMap = mappp; returnnice string; }; 
 
 private：
 static std :: map< int，int> getMap（）{return _myMap; }; 
 
 static std :: map< int，int> _myMap; 
}; 
 
 int main（）{
 
 std :: map< int，int> mappp; 
 
 mappp [1] = 1; 
 
 std :: cout<< MyClass :: niceString（mappp）; 
 
} 
  

错误是：

 错误1错误LNK2001：未解析的外部符号private：static class std :: map< int，int，struct std :: less< int& allocator< struct std :: pair< int const，int>>> MyClass :: _ myMap（？_myMap @ MyClass @@ 0V？$ map @ HHU？$ less @ H @ std @@ V？$ allocator @ U ？$ pair @ $$ CBHH @ std @@@ 2 @@ std @@ A）test22.obj test22 
  

c> c> >

已经声明了静态成员 _myMap ，但是没有定义它。添加此行 int main（）：

  std :: map< int，int> MyClass :: _ myMap; 
  

想象它是一个已声明但未在任何.cpp文件中定义的函数如果您使用链接器错误。

Why do I get linker error when I try to compile this in Visual Studio 2008

#include <stdafx.h>
#include <iostream>
#include <map>
#include <string>

class MyClass
{
public:
 MyClass () { };
 virtual ~MyClass() {};

 static std::string niceString (std::map<int, int> mappp) { _myMap = mappp; return "nice string"; };

private:
 static std::map<int, int> getMap ( ) { return _myMap; };

 static std::map<int, int> _myMap;
}; 

int main(){

 std::map<int, int> mappp;

 mappp[1] = 1;

 std::cout << MyClass::niceString(mappp);

}

error is:

Error 1 error LNK2001: unresolved external symbol "private: static class std::map<int,int,struct std::less<int>,class std::allocator<struct std::pair<int const ,int> > > MyClass::_myMap" (?_myMap@MyClass@@0V?$map@HHU?$less@H@std@@V?$allocator@U?$pair@$$CBHH@std@@@2@@std@@A) test22.obj test22

解决方案

You've declared the static member _myMap, but not defined it. Add this line just above int main():

std::map<int, int> MyClass::_myMap;

Think of it like a function that has been declared but not defined in any .cpp file - you get a linker error if you use it.

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