1. foo.h #ifndef _FOO #define _FOO template <class T> class foo{
private:
T f;
public:
void setFoo(T val);
T getFoo(); };
#endif

2. foo.cpp #include "foo.h" template <class T>
void foo<T>::setFoo(T val){
f = val; }
T foo<T>::getFoo(){
return f;

3. fooImpl.cpp
#include "foo.cpp"
template foo<int>;

4. goodtestFoo.cpp #include <iostream> using namespace std;
#include "fooImpl.cpp"
int main(){
foo<int> myFoo;
myFoo.setFoo(42);
cout << "we got " << myFoo.getFoo() << endl;
return 0; }

5. badTestFoo.cpp #include <iostream> using namespace std;
#include "fooImpl.cpp"
int main(){
foo<int> myFoo;
myFoo.setFoo(42);
cout << "we got " << myFoo.getFoo() << endl;
foo<double> anotherFoo; //OOPS! – not instantiated
anotherFoo.set(64.5);
cout << "we got " << anotherFoo.getFoo() << endl;
return 0; }

6. compile, run goodtestfoo
linux3[106] % g++ -o goodtestfoo goodtestfoo.cpp fooImpl.cpp
linux3[107] % goodtestfoo
we got 42

7. compiling badtestfoo
linux3[104] % g++ -o badtestfoo badtestfoo.cpp fooImpl.cpp
badtestfoo.cpp: In function `int main()':
badtestfoo.cpp:10: no matching function for call to `foo<double>::set(double)'