STL, GCC and explicit template instantiation - c++

Question

Question: Why does the code below not work?
I want to use explicit template instantiation for my project. However, when I try to instantiate a standard algorithm (std::find) it seems like I also need to instantiate some internal routine. It says:
undifined reference to Foo* std::__find<Foo const*, unsigned int>(Foo const*,
Foo const*, unsigned int const&, std::random_access_iterator_tag)
when I
template
Foo* std::find<Foo*,unsigned int>(Foo*,Foo*,const unsigned int&);
More precicly, I am trying to do the following:
#include <algorithm>
#include <cstdio>
class Foo
{
public:
unsigned int id;
bool operator==(unsigned int b)
{return id==b;}
};
template
Foo* std::find<Foo*,unsigned int>(Foo*,Foo*,const unsigned int&);
int main()
{
Foo bar[4]={1,2,3,4};
Foo* p_bar=std::find(bar,bar+4,3);
printf("%p %u\n",p_bar,*p_bar);
return 0;
}
And it compile using
g++ -fno-explicit-templates test.cpp
to force explicit template instantiation.
The compiler output is as follows:
ccWFduTJ.o:test.cpp:(.text$_ZSt4findIP3FoojET_S2_S2_RKT0_[Foo* std::find<Foo*, unsigned int>(Foo*, Foo*, unsigned int const&)]+0x2a): undefined reference to `Foo* std::__find<Foo*, unsigned int>(Foo*, Foo*, unsigned int const&, std::random_access_iterator_tag)'
ccWFduTJ.o:test.cpp:(.text$_ZSt4findIP3FooiET_S2_S2_RKT0_[Foo* std::find<Foo*, int>(Foo*, Foo*, int const&)]+0x2a): undefined reference to `Foo* std::__find<Foo*, int>(Foo*, Foo*, int const&, std::random_access_iterator_tag)'
collect2: ld returned 1 exit status
If it helps, here is what g++ --version outputs:
g++ (tdm-1) 4.5.2
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Answer 1

Just as a quick test, this builds for me:
#include <algorithm>
using namespace std;
class Foo
{
};
template<>
Foo* std::find<Foo*, unsigned int>(Foo*, Foo*, const unsigned int& )
{
return NULL;
}
int main( int argc, char *argv )
{
return 0;
}