C ++ templates Study Notes (3) -- Chapter 4, non-type template parameters

1 Chapter 4 Non-type template parameters

For function templates and class templates, template parameters are not limited to types. common values can also be used as template parameters.

1.1 Non-type class template parameters

For example:

Template <typename T, int maxsize>

Class Stack {

PRIVATE:

T elems [maxsize];

...

};

 

Int main ()

{

Stack <int, 20> int20stack;

Stack <int, 40> int40stack;

...

};

Each template instance has its own type, soInt20stackAndInt40stackThey belong to different types, and there is no explicit or implicit type conversion between these two types; therefore, they cannot be replaced with each other.

 

1.2 Non-type function template parameters

Template<TypenameT,IntVal>

T addvalue (TConst& X)

{

ReturnX + val;

}

STD: vector <Int> SRC;

STD: vector <Int> DEST;

SRC. push_back (1 );

SRC. push_back (2 );

DeST. Resize (5 );

STD: Transform (SRC. Begin (), SRC. End (), dest. Begin (), addvalue <Int, 5>); // 1

The last sentence is written as follows:

STD: Transform (SRC. Begin (), SRC. End (), dest. Begin (), (INT (*) (INT const &) addvalue <Int, 5>); // 2

After my verification in vs2005, you can simply write the 1 style.

1.3 Non-type template parameter restrictions

Generally, a non-type template parameter can be a constant INTEGER (including enumeration) or a pointer to an external linked object.

That is to say, floating point numbers cannot be used, and pointers to internal linked objects cannot be used.

So what is a pointer to an internal link object? The following is an example.

 

Template<Char Const* Name>

ClassMyclass {

...

};

 

Myclass <"Hello"> X;

The"Hello"Is an internal link object, because it is a literal constant. All literal constants are internal link objects.

 

If changed:

Extern Char ConstS [] ="Hello";

Myclass <S> X;

yes.