Undefined reference errors when trying to extend ctype facet

Question

I'm trying to create a custom ctype facet by extending ctype<uint32_t>, but keep getting undefined reference errors.

Here is a minimal test program reproducing the errors:

#include <locale>

using namespace std;

class my_ctype : public ctype<uint32_t> {
public:
    explicit my_ctype(size_t __refs = 0);

protected:
    virtual ~my_ctype();

protected:
    virtual bool do_is(mask __m, char_type __c) const;
    virtual const char_type* do_is(const char_type* __lo, const char_type* __hi, mask* __vec) const;
    virtual const char_type* do_scan_is(mask __m, const char_type* __lo, const char_type* __hi) const;
    virtual const char_type* do_scan_not(mask __m, const char_type* __lo, const char_type* __hi) const;
    virtual char_type do_toupper(char_type __c) const;
    virtual const char_type* do_toupper(char_type* __lo, const char_type* __hi) const;
    virtual char_type do_tolower(char_type __c) const;
    virtual const char_type* do_tolower(char_type* __lo, const char_type* __hi) const;
    virtual char_type do_widen(char __c) const;
    virtual const char* do_widen(const char* __lo, const char* __hi, char_type* __dest) const;
    virtual char do_narrow(char_type __c, char __dfault) const;
    virtual const char_type* do_narrow(const char_type* __lo, const char_type* __hi, char __dfault, char* __to) const;
};

my_ctype::my_ctype(size_t __refs) : ctype<uint32_t>(__refs) {}

my_ctype::~my_ctype() {}

bool my_ctype::do_is(mask __m, char_type __c) const { return false; }
const my_ctype::char_type* my_ctype::do_is(const char_type* __lo, const char_type* __hi, mask* __vec) const { return __hi; }
const my_ctype::char_type* my_ctype::do_scan_is(mask __m, const char_type* __lo, const char_type* __hi) const { return __hi; }
const my_ctype::char_type* my_ctype::do_scan_not(mask __m, const char_type* __lo, const char_type* __hi) const { return __hi; }
my_ctype::char_type my_ctype::do_toupper(char_type __c) const { return __c; }
const my_ctype::char_type* my_ctype::do_toupper(char_type* __lo, const char_type* __hi) const { return __hi; }
my_ctype::char_type my_ctype::do_tolower(char_type __c) const { return __c; }
const my_ctype::char_type* my_ctype::do_tolower(char_type* __lo, const char_type* __hi) const { return __hi; }
my_ctype::char_type my_ctype::do_widen(char __c) const { return __c; }
const char* my_ctype::do_widen(const char* __lo, const char* __hi, char_type* __dest) const { return __hi; }
char my_ctype::do_narrow(char_type __c, char __dfault) const { return __dfault; }
const my_ctype::char_type* my_ctype::do_narrow(const char_type* __lo, const char_type* __hi, char __dfault, char* __to) const { return __hi; }



int main () {
    my_ctype* c = new my_ctype();

    return 0;
}

And here are the errors i'm getting:

Linking console executable: bin\Debug\ctype.exe
obj\Debug\main.o: In function `_ZN8my_ctypeD2Ev':
D:/[...]/ctype/main.cpp:29: undefined reference to `std::ctype<unsigned int>::~ctype()'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x8): undefined reference to `std::ctype<unsigned int>::~ctype()'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0xc): undefined reference to `std::ctype<unsigned int>::~ctype()'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x10): undefined reference to `std::ctype<unsigned int>::do_is(unsigned short, unsigned int) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x14): undefined reference to `std::ctype<unsigned int>::do_is(unsigned int const*, unsigned int const*, unsigned short*) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x18): undefined reference to `std::ctype<unsigned int>::do_scan_is(unsigned short, unsigned int const*, unsigned int const*) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x1c): undefined reference to `std::ctype<unsigned int>::do_scan_not(unsigned short, unsigned int const*, unsigned int const*) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x20): undefined reference to `std::ctype<unsigned int>::do_toupper(unsigned int) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x24): undefined reference to `std::ctype<unsigned int>::do_toupper(unsigned int*, unsigned int const*) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x28): undefined reference to `std::ctype<unsigned int>::do_tolower(unsigned int) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x2c): undefined reference to `std::ctype<unsigned int>::do_tolower(unsigned int*, unsigned int const*) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x30): undefined reference to `std::ctype<unsigned int>::do_widen(char) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x34): undefined reference to `std::ctype<unsigned int>::do_widen(char const*, char const*, unsigned int*) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x38): undefined reference to `std::ctype<unsigned int>::do_narrow(unsigned int, char) const'
obj\Debug\main.o:main.cpp:(.rdata$_ZTVSt5ctypeIjE[vtable for std::ctype<unsigned int>]+0x3c): undefined reference to `std::ctype<unsigned int>::do_narrow(unsigned int const*, unsigned int const*, char, char*) const'
collect2.exe: error: ld returned 1 exit status
Process terminated with status 1 (0 minutes, 1 seconds)
15 errors, 1 warnings

I looked into locale_facets.h and found out that there are template specializations for ctype<char> and ctype<wchar_t>, and I'm afraid that I might have to create a specialization for uint32_t as well, but I just can't see why.

So here are my questions:

1 - Why am I getting those error messages?

2 - How do I fix it?

3 - If I do have to specialize ctype<> for uint32_t, why is that the case?

I'm compiling my program with mingw on windows, through CodeBlocks. The test program is only main.cpp, no other files.

Answer 1

1. Because there is no specialization for uint32_t
2. write a specialization
3. Base class must be implemented

Consider the code below

class A {
public:
virtual void func(); // no implementation here virtual ~A();
}; class B : public A
{
public:
virtual void func() {}
};

Instance of B can not be created.

Answer 2

my problem was not having a constructor, hope that helps someone!