决仕~上班族

    Here, as we know, the generic programming has become a trend in the programming langauge design. C++ offers a good support to generic programming from its very begenning. The template methodology is such an example. You can write a template function to adopt variant type parameters. You can design a template class to have a common interface and relealize the dream of "write once and use much times". The STL which means standard Template Library and the algorithms are the applications of such methodology.

    But in VC++, the template class's declaration and defenition that is often the source code must be in the same file, or else it will not pass compile progress, and the compile error message is external symbols can not be resolved, just like we use a external variant in the function without using external directive for the very variant. I remember this question happened before when I was a undergraduate. But the template function has no such question. Surprised? Maybe.

    Below is just a sample, you can try it if you are interested in it:
//stu.h
namespace jazz
{
 template<typename Type> class Array
 {
 public:
  Array(int size_);
  ~Array() throw();
  Type& operator[](int index);
  void dump();
 private:
  Type* data;
  size_t size;
 };

 template<typename Type> Array<Type>::Array(int size_) try: size(size_),data(new Type[size_])
 {
 }catch(std::bad_alloc& e)
 {
  throw;
 }
 template<typename Type> Type& Array<Type>::operator [](int index)
 {
  if(index<0 || index>= size)
   throw std::out_of_range("script index is out of range");
  return data[index];
 }

 template<typename Type> Array<Type>::~Array() throw()
 {
  delete[] data;
 }
 template<typename Type> void Array<Type>::dump()
 {
  for(int i=0;i<size;i++)
   cout<<data[i]<<endl;
 }
}
//there is no error above
------------------------------------------
//stu.h
namespace jazz
{
 template<typename Type> class Array
 {
 public:
  Array(int size_);
  ~Array() throw();
  Type& operator[](int index);
  void dump();
 private:
  Type* data;
  size_t size;
 };
}
//stu.cpp
namespace jazz
{
template<typename Type> Array<Type>::Array(int size_) try: size(size_),data(new Type[size_])
 {
 }catch(std::bad_alloc& e)
 {
  throw;
 }
 template<typename Type> Type& Array<Type>::operator [](int index)
 {
  if(index<0 || index>= size)
   throw std::out_of_range("script index is out of range");
  return data[index];
 }

 template<typename Type> Array<Type>::~Array() throw()
 {
  delete[] data;
 }
 template<typename Type> void Array<Type>::dump()
 {
  for(int i=0;i<size;i++)
   cout<<data[i]<<endl;
 }
}
//there is compile error above