Linker complains about undefined reference on vtable

I have this code in my fileType.h.

class FileType{
    private:
        School* m_school;
        string m_fileFormat;
        const string m_cfgFile;
        const string m_inputFile;

    public:
        FileType(string p_fileFormat, string p_cfgFile, string p_inputFile):
                 m_fileFormat(p_fileFormat), m_cfgFile(p_cfgFile), m_inputFile(p_inputFile) {};
        virtual bool parseInputFile();
        virtual bool writeOutputFile(const School& m_school);
        virtual bool checkFormat(); // TBD -- used to check the format of the input file
        virtual bool checkConstraints(); // TBD -- used to check things like only +ve 12 digit in the ID etc
        virtual ~FileType();
};

class XmlType:public FileType{

    public:
        XmlType(string p_fileFormat, string p_cfgFile, string p_inputFile):
            FileType(p_fileFormat, p_cfgFile, p_inputFile) {};
        virtual bool parseInputFile();
        virtual bool writeOutputFile(const School& m_school);
        virtual bool checkFormat(); // TBD -- used to check the format of the input file
        virtual bool checkConstraints(); // TBD -- used to check things like only +ve 11 digit in the ID etc

};


class CsvType:public FileType{

    public:
        CsvType(string p_fileFormat, string p_cfgFile, string p_inputFile):
            FileType(p_fileFormat, p_cfgFile, p_inputFile) {};
        virtual bool parseInputFile();
        virtual bool writeOutputFile(co开发者_如何学Pythonnst School& m_school);
        virtual bool checkFormat(); // TBD -- used to check the format of the input file
        virtual bool checkConstraints(); // TBD -- used to check things like only +ve 11 digit in the ID etc

};

In my main I put in :

#include "fileType.h"

    FileType *inputFilePtr, *outputFilePtr;
    string stringOne, stringTwo, stringThree;
    inputFilePtr = new CsvType(stringOne, stringTwo, stringThree);

Now my linker tells me that I does not know about the symbols for constructors:

/cygdrive/c/Users/Owner/AppData/Local/Temp/cclieUAi.o:main.cpp:(.text$_ZN7CsvTypeC1ESsSsSs[CsvType::CsvType(std::basic_string, std::allocator >, std::basic_string, std::allocator >, std::basic_string, std::allocator >)]+0x1bf): undefined reference to vtable for CsvType' /cygdrive/c/Users/Owner/AppData/Local/Temp/cclieUAi.o:main.cpp:(.text$_ZN8FileTypeC2ESsSsSs[FileType::FileType(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)]+0x3a): undefined reference tovtable for FileType' collect2: ld returned 1 exit status

I tried making a dummy constructor with two ints and doing nothing. That worked, but once I put strings, this fails. Any idea what is wrong?

You've defined only the constructors, but you've not defined the virtual functions. Only declaring them is not enough. You've to define them as well, which means, the function should have function-body, containing some statements (though it can be blank as well).

//file.h
class A
{ 
   virtual void f(); //this is called declaration
};

//file.cpp
void A::f() //this is called definition
{
  //this is called function-body.
}

you declared the virtual destructor but your subclasses don't have one!

where is virtual ~CsvType() { } and virtual ~XmlType() {}

if this is an abstract base class you might consider setting the functions of FileTypeto purely virtual by virtual bool parseInputFile() = 0; so that you can't construct an object of FileType.

Also after virtual bool parseInputFile() {} you don't require a ;