A Template in C++ is a mold for an algorithm along with the
template function that can operate on a generic datatype, which will allow you
to use the same function on many different types of data. The T in template<
class T > is a generic datatype.
Template class is an entire class that operates on a generic
datatype. You also have to be careful what you name the generic class and
regular class, Example: if you have a generic class named myGeneric and a
regular class also named myGeneric, then you are going to get errors. A non-templated
class organization tends to be messy because you almost never have all of the
classes in the same file. Templates do not have to be based on a single generic
datatype so you can have parameterized datatypes.
The compiler analyzes the datatypes that are passed into the
function and creates the appropriate template based on the return value. C++
also allows you to use values of a particular datatype. Template classes with
different value parameters are considered totally different types, also doubles
are twice as large as ints.
A value parameter could be of a generic datatype. Templates
though are limited. If you try to program templates in the way using .h and
.cpp files in MSVC6, it will give you errors.
C++ goes through the template definition, copies the code,
and replaces every instance of the parameterized type name with the actual type
name. The compiler performs the copying for you automatically when you compile
the program so that you don’t have to do it manually.
A template is nothing more than a copied-and-pasted bunch of
code, the compiler does all the work for you. Therefore, you can write a really
fast algorithm and have it run at full speed for every datatype you want.
For me, templates at first was a little bit confusing. But
after some research and time put into it, they are becoming easier and easier.
Source:
Data Structures for Game Programmers: Ron Penton and Andre
LaMothe, pp. 14-36
