c++ - 从多个文件编译得到 “undefined reference”

Question

我需要在单独的文件中提供CFG类，但是我不确定如何将其与相关的.h和主程序一起编译。

我已经将.h文件#include编码了，并且我已经在命令行中请求了这两个文件，但是我不确定为什么将它们一起编译是错误的。

有什么想法吗？

CFG.cpp:

#include <iostream>
#include <stdio.h>
#include <string>

using namespace std;

class CFG
{
    public:
        string code[25];
        char startNT;
    //private:

    CFG(string inCode[], int stringLen)
    {
        for (int a = 0; a < stringLen; a++)
        {
            //cout << inCode[a] << endl;
            this->code[a] = inCode[a];
        }
        for (int a = 0; a < stringLen; a++)
        {
            cout << this->code[a] << endl;
        }
    }

    char getStartNT()
    {
        return startNT;
    }

    void setStartNT(char stNT)
    {
        startNT = stNT;
    }

    bool processData(string inString, string wkString)
    {
        //Our recursive function
        return true;
    }

    void garbage()
    {
        return;
    }
};

CFG.h:

#ifndef _cfg_h_
#define _cfg_h_

#include <iostream>
#include <stdio.h>
#include <string>

using namespace std;

class CFG
{
    public:
        string code[25];
        char startNT;

        CFG(string inCode[], int stringLen);
        char getStartNT();
        void setStartNT(char stNT);
        bool ProcessData(string inString, string wkString);
        void garbage();
};

#endif

cfg_entry.cpp:

#include <stdio.h>
#include <iostream>
#include "cfg.h"

using namespace std;

int main()
{
    string inArray[5];
    inArray[0] = "test0";
    inArray[1] = "test1";
    inArray[2] = "test2";
    inArray[3] = "test3";
    inArray[4] = "test4";
    CFG * cfg1 = new CFG(inArray, 5);
    cfg1->garbage();
    return 0;
}

编译错误:

art@tv:~/Dropbox/Weber/CS 4110/Individual Assignment 2$ g++ -g -std=c++11 -Wall -o cfg_entry cfg.cpp cfg_entry.cpp
/tmp/ccICQEd0.o: In function `main':
/home/art/Dropbox/Weber/CS 4110/Individual Assignment 2/cfg_entry.cpp:15: undefined reference to `CFG::CFG(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, int)'
/home/art/Dropbox/Weber/CS 4110/Individual Assignment 2/cfg_entry.cpp:16: undefined reference to `CFG::garbage()'
collect2: error: ld returned 1 exit status

Answer 1

我发现了我的问题。在我的情况下，头文件定义了类，.cpp文件再次重新定义了它，试图创建2个CFG类实例。 .h需要处理类声明和变量实例化，而.cpp仅处理函数定义。

cfg.h:

#ifndef _cfg_h_
#define _cfg_h_

#include <iostream>
#include <stdio.h>
#include <string>

using namespace std;

class CFG
{
    private:
        string code[25];
        char startNT;

    public:
        CFG(string inCode[], int stringLen);
        char getStartNT();
        void setStartNT(char stNT);
        bool processData(string inString, string wkString);
        void garbage();
};

#endif

cfg.cpp:

#include <iostream>
#include <stdio.h>
#include <string>
#include "cfg.h"

using namespace std;

CFG::CFG(string inCode[], int stringLen)
{
    for (int a = 0; a < stringLen; a++)
    {
        //cout << inCode[a] << endl;
        this->code[a] = inCode[a];
    }
    for (int a = 0; a < stringLen; a++)
    {
        cout << this->code[a] << endl;
    }
}

char CFG::getStartNT()
{
    return startNT;
}

void CFG::setStartNT(char stNT)
{
    startNT = stNT;
}

bool CFG::processData(string inString, string wkString)
{
    //Our recursive function
    return true;
}

void CFG::garbage()
{
    return;
}