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This article introduces the knowledge of "what is the variable template parameter in the difficulty analysis of the new C++ standard". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Preface

C++ 's new feature-variable template parameters (variadic templates) is one of the most powerful new features of C++. It highly generalizes the parameters and can represent 0 to any number of parameters of any type. Compared with Category 98amp 03, class templates and function templates can only contain a fixed number of template parameters, variable template parameters is undoubtedly a great improvement. However, because the variable template parameters are abstract and require some skills to use, it is also one of the most difficult features in C++ to understand and master. Although it is difficult to master variable template parameters, it is one of the most interesting features in Cellular template 11.

Expansion of variable template parameters

The semantics of the variable parameter template is the same as that of the ordinary template, except that it is slightly different in writing. When declaring a variable parameter template, you need to put an ellipsis "..." after typename or class. For example, we often declare a variable template parameter: template

Template void f (T... Args)

The role of the ellipsis:

1. Declare a parameter package T... Args, this parameter package can contain 0 to any template parameters; 2. On the right side of the template definition, you can expand the parameter package into a separate parameter.

The parameter of the ellipsis is called the "parameter package", which contains 0 to N (N > = 0) template parameters. We can not get every parameter in the parameter package args directly, we can only obtain each parameter in the parameter package by expanding the parameter package, which is one of the main characteristics of using variable template parameters, and it is also the biggest difficulty, that is, how to expand variable template parameters.

Variable template parameter classification:

1. Variable template parameter function

two。 Variable template parameter class

Print the number of parameters of the variable template parameter function

# include # include using namespace std; template void print (Type... data) {cout

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