Menu
Template in C++is a feature. We write code once and use it for any data type including user defined data types. For example, sort() can be written and used to sort any data type items. A class stack can be created that can be used as a stack of any data type.
The act of creating a new definition of a function, class, or member of a class from a template declaration and one or more template arguments is called template instantiation. The definition created from a template instantiation is called a specialization.
Instead the programmer can write a C++ template based function that will work with all data types. There are two types of templates in C++, function templates and class templates.
A template allows us to create a family of classes or family of functions to handle different data types. Template classes and functions eliminate the code duplication of different data types and thus makes the development easier and faster. Multiple parameters can be used in both class and function template.
Intuitively, when you fully specialize something, it doesn't depend on a template parameter any more -- so unless you make the specialization inline, you need to put it in a .cpp file instead of a .h or you end up violating the one definition rule as David says. Note that when you partially specialize templates, the partial specializations do still depend on one or more template parameters, so they still go in a .h file.
The keyword inline is more about telling the compiler that the symbol will be present in more than one object file without violating the One Definition Rule than about actual inlining, which the compiler can decide to do or not to do.
The problem you are seeing is that without the inline, the function will be compiled in all translation units that include the header, violating the ODR. Adding inline there is the right way to go. Otherwise, you can forward declare the specialization and provide it in a single translation unit, as you would do with any other function.
You've explicitly instantiated a template in your header (void Hello<T>::print_hello(T var)). This will create multiple definitions. You can solve it in two ways:
1) Make your instantiation inline.
2) Declare the instantiation in a header and then implement it in a cpp.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With