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Templates in C++


Templates have been helping programmers to change the way they are able to code since the ealy 1990s. Since that time they have advanced rapidly, and in this tutorial we will take a close look at them and learn to use them to effectively decrease our tasks.

Author Info:
By: Gabor Bernat
Rating: 3 stars3 stars3 stars3 stars3 stars / 9
June 17, 2008
TABLE OF CONTENTS:
  1. · Templates in C++
  2. · Starting with Templates
  3. · Class Templates
  4. · Template Specialization

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Templates in C++ - Template Specialization
(Page 4 of 4 )

Furthermore, you can specify an individual implementation for a class for which you want a specific solution. Maybe you are creating a class that, even though it is general, it has an exception -- a situation that you need to treat separately. This can be resolved through template specialization. And the method used to complete this is the following specialization-let's go back to the function template because it's more didactic and shorter:

template<>

int function<char>( char first, char second)

{

return first > second ? first : second;

 

}

Using the written method is nothing devilish, just as usual you would use:

char a = 'A';

char b = 'B';

char result;

result =static_cast<char> ( function(a, b));

cout << result << endl;

result =static_cast<char> ( function(b, a));

cout << result << endl;

The upper code snippet will print the character that is higher by ASCII code to the console (cout). So this will be the 'B' character twice. If you paid attention, by now you should also realize that the static_cast function is a template, and one that is called to the type you specify between the <>. As mentioned previously, this can be done for classes too and the method is the same.

There is one more thing we should mention. You may want to add non-type parameter(s) to your template. This consists of adding a type as a parameter in the template. Back to the initial problem:

template< int Number ,typename Type,class T >

int function( Type first, T second)

{

 

return memcmp(&first, &second,sizeof(first)*Number);

}

And using it shouldn't be a problem to understand:

char a = 'A';

char b = 'B';

int result;

result = function< 0>(a, b);

cout << result << endl;

result = function<1, char, char>(a, b);

cout << result << endl;

Basically, you give a constant to the function at function call. The number variable is a constant within the function (or the class if you write it for it) and can't be changed in the code snippet inside the function. This makes it expedient to use this method each time you need to initialize a value in a template.

For example, if you want to create a class that has Number length strings/arrays within it, you can do this by passing the size of the string at creation. Of course, in various other places, just use your imagination. For class templates, you may also add default values for non-type parameters. You are only forced to give the number parameter because the rest can be deduced by the compiler. However, if you write it explicitly in the code, the compiler won't mind at all.

Conclusion

We've arrived at the end and by now you should know everything to be known about template class creation. You should become a genuine expert with just a little practice. Please don't forget that programming is just like love, you can't learn it from books. In order to understand it, you must make a move. Start up your compiler and write a couple of lines. See the problems, try them and don't forget: don't hesitate because affirmation without act means nothing.

Now may be the perfect time to get a good introduction into the libraries I mentioned at the beginning. The STL is a perfect place to start. Check out the "Introduction to STL," which will be published on Dev Articles.

See you next time, and if you have any questions regarding the things we learned so far, feel free to ask in the forums. This is a place for a community where evolution is present at every second, and you can join in. Have a nice weekend and keep on coding!


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