Difference between instantiation and specialization in c++ templates

Question

What is the difference between specialization and instantiation in context of C++ templates. From what I have read so far the following is what I have understood about specialization and instantiation.

template <typename T> struct Struct {       T x; };  template<> struct Struct <int> //specialization {      //code };  int main() {    Struct <int> s; //specialized version comes into play    Struct <float> r; // Struct <float> is instantiated by the compiler as shown below  } 

Instantiation of Struct <float> by the compiler

template <typename T=float> struct Struct {     float x; } 

Is my understanding of template instantiation and specialization correct?

Answer 1

(Implicit) Instantiation

This is what you refer to as instantiation (as mentioned in the Question)

Explicit Instantiation

This is when you tell the compiler to instantiate the template with given types, like this:

template Struct<char>; // used to control the PLACE where the template is inst-ed 

(Explicit) Specialization

This is what you refer to as specialization (as mentioned in the Question)

Partial Specialization

This is when you give an alternative definition to a template for a subset of types, like this:

template<class T> class Struct<T*> {...} // partial specialization for pointers 

Answer 2

What is the difference between specialization and instantiation in context of C++ templates?

Normally (no specializations present) the compiler will create instantiations of a template when they are used, by substituting actual template parameters (int in your example) for the formal template parameters (T) and then compile the resulting code.

If a specialization is present, then for the (set of) special template parameter(s) specified by that specialization, that specialization's implementation is to be used instead of what the compiler would create.