c++ template errors: undefined reference to `operator<< ...

[bryan.taylor]

I'm attempting to make a small set of logging classes, but for the final piece (for now) I keep getting the following error:

undefined reference to `operator<<(MBBMultipleOstream&, char const*)'
I have code in a header file (mbb_logger.h):

class MBBMultipleOstream : public std::ostream
{
public:
friend MBBMultipleOstream &operator<<(MBBMultipleOstream &, const char *);

public:
MBBMultipleOstream() :
std::ios(0),
std::ostream(&mEmptyStreambuf)
{}

void AddOstream(std::ostream &os)
{
mOstreams.push_back(&os);
}

template <class T>
void Write(T item)
{
for (size_t i = 0; i < mOstreams.size(); i++) {
(*mOstreams[i]) << item;
}
}

private:
std::vector <std::ostream *> mOstreams;

MBBEmptyStreambuf mEmptyStreambuf;
};

template <class T>
MBBMultipleOstream &operator<<(MBBMultipleOstream &os, T item)
{
os.Write(item);
return os;
}

and when I try to use it in main(...) i get the above error:

MBBMultipleOstream mos;
mos.AddOstream(std::cout);
mos.AddOstream(std::cerr);
mos << "foo\n";
mos << "bar\n";

If I explicitly create the following function instead of using the template everything works fine:

MBBMultipleOstream &operator<<(MBBMultipleOstream &os, const char *item)
{
os.Write(item);
return os;
}

Does anyone have any ideas?

I imagine that the code above is rather kludgy, but I don't know iostreams very well, so I'm open to suggestions about how to make the code better. :)

[fifo]

I think the non-template friend declaration might be the culprit. The following works fine for me:

#include <iostream>
#include <vector>

class MBBMultipleOstream
{
public:
MBBMultipleOstream()
{}

void AddOstream(std::ostream &os)
{
mOstreams.push_back(&os);
}

template <class T>
void Write(T item)
{
for (size_t i = 0; i < mOstreams.size(); i++) {
(*mOstreams[i]) << item;
}
}

private:
std::vector <std::ostream *> mOstreams;
};

template <class T>
MBBMultipleOstream &operator<<(MBBMultipleOstream &os, T item)
{
os.Write(item);
return os;
}

int main()
{
MBBMultipleOstream mos;
mos.AddOstream(std::cout);
mos.AddOstream(std::cerr);
mos << "foo\n";
mos << "bar\n";
return 0;
}

[bryan.taylor]

Thanks, that worked perfectly. :)