链接器 2001 成员变量的错误和未定义的标识符

问：

差不多完成了这个程序，在移动到公共计算机并更改了一些代码后，我注意到我收到了一个链接器错误，我还决定询问另一个错误（以及为什么会发生）。

有问题的函数如下。出于某种原因，最后一行“ValidTlds[transferString]....”显示 VS 无法识别 ValidTLD，并且只有在我在其后面添加 TldPart：：（它所在的文件的名称）时才会识别。这个名字是否与其他名称冲突？

此外，我认为更重要的错误也涉及函数，是未解析的外部符号。确切的线路：

Error   3   error LNK2001: unresolved external symbol "public: static class std::map<class String,class String,struct std::less<class String>,class std::allocator<struct std::pair<class String const ,class String> > > TldPart::ValidTlds" (?ValidTlds@TldPart@@2V?$map@VString@@V1@U?$less@VString@@@std@@V?$allocator@U?$pair@$$CBVString@@V1@@std@@@3@@std@@A)    V:\My Documents\Visual Studio 2010\Projects\EmailChecker_HW2\EmailChecker_HW2\TldPart.obj

我试着阅读了你关于外部符号的问答页面，并尝试了一些建议（最初我有两个），我设法通过在类外声明静态函数来减少它，我相信这是一个链接器错误。你们看到怎么了？在主要.cpp中，我将该函数引用为“TldPart：:P reloadTLDs;”，但删除该行并没有删除错误（我在主.cpp文件的顶部 #include“TldPart.h”）。这是函数，我将在下面发布标题和 cpp 文件以供完整参考。整个项目非常广泛（我上次检查了近 1100 行），所以我只包括这些作为初学者。感谢您的帮助，我很感激。

static void 预加载TLDs（）

static void PreloadTLDs()
{
    bool initialized = false;
    bool fileStatus = false;
    string tldTest = ""; // used for getline() as allowed.
    char * transferString = " "; // used to transfer chars from string to String

    ifstream infile;

    infile.open("ValidTLDs.txt");

    fileStatus = infile.good();

    if(fileStatus != true)
        cout << "Cannot read ValidTLD's file. Please check your file paths and try again.";
    else
    {
        while(!infile.eof())
        {
            getline (infile, tldTest); // sets the current TLD in the list to a string for comparision

            // converts TLD to lowercase for comparison.
            for(unsigned int x = 0; x<tldTest.length(); x++)
            {
                tldTest[x] = tolower(tldTest[x]);
                transferString[x] = tldTest[x];

                ValidTlds[transferString] = String(transferString);
            }
        }
    }
}

main.cpp （缩短）

#include <iostream>
#include <fstream>
#include "String.h"
#include <map>
#include <string> // used for the allowed getline command
#include "Email.h"
#include "TldPart.h"

using namespace std;

void main()
{
    string getlinetransfer; // helps transfer email from getline to c string to custom String
    double emailTotal = 0.0; // Used to provide a cool progress counter
    double emailCounter = 0.0; // Keeps track of how many emails have been verified.
    int x = 0; // used to set c-string values, counter for loop
    char * emailAddress = new char[getlinetransfer.size() + 1]; // c string used for getting info from getline.

    cout << "Welcome to email validation program!" << endl;
    cout << "Pre-Loading Valid TLD's..... \n" << endl;

    TldPart::PreloadTLDs;
}

TldPart.h

// TldPart.h - TldPart validation class declaration
// Written by ------

#pragma once

#include "String.h"
#include <map>
#include "SubdomainPart.h"
#include <string>
#include <fstream>
#include <iostream>

using namespace std;



class TldPart
{
public:
    // MUST HAVE a defualt constructor (because TldPart is a member of Domain)
    TldPart() {}

    // Takes the address and stores into the Address data member
    void Set(const String& address);

    static void PreloadTLDs();

    // Returns true when the Address is valid or false otherwise
    bool IsValid();

    static map<String, String> ValidTlds;
private:
    String Address; 
};

TldPart.cpp

// TldPart.cpp - TldPart validation class implementation
// Written by Max I. Fomitchev-Zamilov

#pragma once

#include "TldPart.h"
using namespace std;

void TldPart()
{

}

// Takes the address and stores into the Address data member
void TldPart::Set(const String& address)
{
    Address = address;
}

static void PreloadTLDs()
{
    bool initialized = false;
    bool fileStatus = false;
    string tldTest = ""; // used for getline() as allowed.
    char * transferString = " "; // used to transfer chars from string to String

    ifstream infile;

    infile.open("ValidTLDs.txt");

    fileStatus = infile.good();

    if(fileStatus != true)
        cout << "Cannot read ValidTLD's file. Please check your file paths and try again.";
    else
    {
        while(!infile.eof())
        {
            getline (infile, tldTest); // sets the current TLD in the list to a string for comparision

            // converts TLD to lowercase for comparison.
            for(unsigned int x = 0; x<tldTest.length(); x++)
            {
                tldTest[x] = tolower(tldTest[x]);
                transferString[x] = tldTest[x];

                ValidTlds[transferString] = String(transferString);
            }
        }
    }
}

// Returns true when the Address is valid or false otherwise
bool TldPart::IsValid()
{   
    bool tldFound = false;

    map<String, String>::iterator it;

    String TLDMatch;

    TLDMatch = TldPart::ValidTlds.find(Address)->first;
    it = TldPart::ValidTlds.find(Address);

    if(it == ValidTlds.end())
        tldFound == false;
    else
        tldFound == true;

    return tldFound;
}