Question

State which of the following statements are true and which are false. If a statement is \(f a / s e,\) explain why. a. The template parameters of a function-template definition are used to specify the types of the arguments to the function, to specify the return type of the function and to declare variables within the function. b. Keywords typename and class as used with a template type parameter specifically mean "any user-defined class type." c. A function template can be overloaded by another function template with the same function name. d. Template parameter names among template definitions must be unique. e. Each member-function definition outside a class template must begin with a template header. f. A friend function of a class template must be a function-template specialization. g. If several class-template specializations are generated from a single class template with a single static data member, each of the classtemplate specializations shares a single copy of the class template's static data member.

Short answer

a. False; b. False; c. True; d. False; e. True; f. False; g. False.

Step-by-step solution

Analyze Statement A

The statement claims that template parameters are used to specify argument types, return types, and declare variables within a function. This statement is incorrect because template parameters are not used to declare variables within the function. They are mainly used for specifying types for arguments and return types, not for declaring variables.

Analyze Statement B

The keywords `typename` and `class`, when used in templates, refer to any type, not just user-defined class types. They can include primitive types, user-defined classes, and more. Thus, the statement is incorrect.

Analyze Statement C

Function templates can indeed be overloaded by other function templates with the same name but different parameter lists, much like normal function overloading. Thus, this statement is true.

Analyze Statement D

In different template definitions, template parameter names do not need to be unique. They are scoped within their respective templates. Thus, this statement is incorrect.

Analyze Statement E

Each member-function definition outside a class template must indeed begin with a template header, specifying the template parameters. Thus, this statement is true.

Analyze Statement F

A friend function of a class template does not necessarily need to be a function template specialization; it can be a regular function. Thus, this statement is incorrect.

Analyze Statement G

If several class-template specializations are generated from a class template, each specialization has its own static data member. They do not share one instance unless explicitly stated, making this statement incorrect.

Key concepts

Function Templates

In C++, function templates are a powerful feature that allows programmers to create generic functions. This means that you can write a single function template that works with any data type without having to write multiple separate functions for each data type. When using function templates, you define a template with the keyword `template` followed by template parameters enclosed in angle brackets, \(< >\). These parameters are placeholders for actual data types.
For example, a simple function template for calculating the maximum of two values might look like this:

• `template `
• `T max(T a, T b) { return (a > b) ? a : b; }`

In this function template, the type `T` acts as a placeholder for any data type. When calling this function with different data types, such as integers or floating-point numbers, the compiler generates a specific version of the function for each data type used. Naturally, this enables code reusability, saving time and reducing code redundancy.

Class Templates

Class templates are similar to function templates but are used to create classes that can operate with generic data types. With class templates, you define the operations that the class will perform with any type of data without binding it to specific data types upfront. This allows for the creation of flexible and reusable classes.
To define a class template, you use the `template` keyword followed by the template parameters, much like with function templates. Here's a basic example of a class template for a simple pair of values:

• `template `
• `class Pair {`
• `public:`
• `Pair(T1 first, T2 second) : first_(first), second_(second) {}`
• `T1 GetFirst() { return first_; }`
• `T2 GetSecond() { return second_; }`
• `private:`
• `T1 first_;`
• `T2 second_;`
• `};`

In this example, `Pair` is a class template that holds two values of potentially different types, indicated by `T1` and `T2`. This approach greatly enhances the adaptability and reusability of C++ classes.

Template Parameters

Template parameters are crucial elements of C++ templates, defining the blueprint for the data types to be used in templates. They act as placeholders in both function and class templates and are essential in creating flexible and reusable code. When creating a template, the parameters specify the types or constants that the function or class will work with.
There are primarily two types of template parameters:

• **Type Parameters**: Indicated by `typename` or `class`, these specify that a placeholder is meant for data types.
• **Non-type Parameters**: These represent values, such as integers, which can also be used as template parameters. For instance, specifying the size of a static array could be done through a non-type parameter.

Template parameters are defined at the beginning of the template with the `template` keyword. This process creates a template that the compiler can generate into a specific instance once the exact types or values are known. This flexibility enhances code adaptability significantly.

Template Specializations

Template specialization in C++ refers to the ability to define a specific implementation of a template for a particular set of template arguments. This feature allows fine-tuning and optimizing templates for specific cases where the generic implementation may not be the most efficient or suitable.
Two types of template specializations exist:

• **Full Specialization**: Here, you define a template specifically for a certain data type, such that it differs completely from the general template. This is used when the behavior for the specific type is distinctively different.
• **Partial Specialization**: This applies mainly to class templates, where only part of the template parameters are specialized, allowing customization while still maintaining some level of generality.

For example, consider a class template for handling arrays. While you might have a general implementation, a specialization for arrays of type `char` could handle null-terminated strings more efficiently.
Template specializations thus provide crucial control over template behavior, ensuring that specific cases can be handled correctly and with optimal performance.