C++ "fatal error LNK1120"未解析的静态类成员

Question

我收到以下错误消息(有人可以随意编辑不必要的位):

1>FIXDecoder.obj : error LNK2001: unresolved external symbol "private: static class std::unordered_map,class std::allocator >,class std::basic_string,class std::allocator >,struct std::hash,class std::allocator > >,struct std::equal_to,class std::allocator > >,class std::allocator,class std::allocator > const ,class std::basic_string,class std::allocator > > > > FD::FixValueMappingsDict" (?FixValueMappingsDict@FD@@0V?$unordered_map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@@std@@@2@@std@@A)

1>FD.obj : error LNK2001: unresolved external symbol "private: static class std::unordered_map,class std::allocator >,class std::basic_string,class std::allocator >,struct std::hash,class std::allocator > >,struct std::equal_to,class std::allocator > >,class std::allocator,class std::allocator > const ,class std::basic_string,class std::allocator > > > > FD::FIXFieldNoDict" (?FIXFieldNoDict@FD@@0V?$unordered_map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@@std@@@2@@std@@A)

1>C:\visual studio 2012\Projects\FD\x64\Debug\FD.exe : fatal error LNK1120: 2 unresolved externals

对于这段代码:

//FH.h
#ifndef FD_H
#define FD_H

#include "FM.h"
#include <unordered_map>
#include <string>

class FD{
public:
    FD();
    FD(FM message);
    ~FD();
    FD(const FD& tocopy);
    FD& operator=(const FD& toassign);

private:
    static unordered_map<string,string> FIXFieldNoDict;
    static unordered_map<string,string> FixValueMappingsDict;
};

#endif

//FD.cpp
#include "FD.h"
#include "Mappings.h"
#include "Utils.h"
#include <vector>
#include <string>
#include <iostream>
#include <unordered_map>

using namespace std;

FD::FD(){
    FIXFieldNoDict = Mappings::createFIXFieldNoDict();
    FixValueMappingsDict = Mappings::getFIXValuesDict();
}

Mappings.h 只包含一些创建 unordered_map 的函数

#ifndef MAPPINGS_H
#define MAPPINGS_H

#include <unordered_map>
#include <string>

using namespace std;

class Mappings{

public:
    Mappings();

    static unordered_map<string,string> createFIXFieldNoDict();

    static unordered_map<string,string> getFIXValuesDict();
.
.
};

Answer 1

您需要在 FD.cpp 文件中创建静态成员的实例:

//FD.cpp
#include "FD.h"
#include "Mappings.h"
#include "Utils.h"
#include <vector>
#include <string>
#include <iostream>
#include <unordered_map>

using namespace std;

unordered_map<string,string> FD::FIXFieldNoDict = Mappings::createFIXFieldNoDict();
unordered_map<string,string> FD::FixValueMappingsDict = Mappings::getFIXValuesDict();


FD::FD(){
}

请注意，您不应该在 FD 构造函数中初始化它们，因为您可以在构造任何对象之前使用静态成员(并且您需要初始化它们一次，而不是每次当某个对象被初始化时构造)。