C++ Type Traits
The C++ standard library's C++ type traits are a powerful feature that offers compile-time information about the properties of types. They provide more flexible and generic programming by allowing type queries and manipulation during compilation. Type traits let you write more expressive, effective, and robust code because they let you build template code that can change to fit different types without degrading performance.
In modern C++ programming, type traits are crucial, especially in fields like template metaprogramming and generic programming. They enable you to use the C++ type system's power to make choices and carry out operations depending on type properties.
Syntax:
#include <type_traits>
Types of C++ Type Traits
Type traits are divided into different types, each of which has a specific function and are frequently used as template classes or template functions:
- Primary Type Traits: These describe a type's essential characteristics, such as whether it is a pointer, reference, array, or a basic type like int or float. Is_pointer, Is_reference, and Is_array are a few examples.
- Composite-type traits: These composite-type qualities are used to combine or alter existing traits. For instance, add_const adds a const qualifier to a type, whereas remove_pointer removes any pointer qualifiers from a type.
- Type property queries: These qualities include details about the characteristics of types, such as whether they are enum types, have a specific size, or are trivially copyable. Examples include extent, is_enum, and is_trivially_copyable.
- Type relationship traits: These characteristics, such as whether one type can be changed into another or whether a type originates from another, assist you in figuring out the links between them. Is_convertible, Is_base_of, and Is_Same are a few examples.
- Type transformation traits: Type transformation features let you change types in various ways, such as adding a type pointer or eliminating references. Decay, add_pointer, and remove_reference are a few examples.
Primary Type Traits
- is_void<T>: Whether type T is a void type is determined by this trait. It is helpful when designing specialized behavior or handling void types, such as in template metaprogramming.
- is_null_pointer<T>: It establishes whether the type T is a nullptr_t. This function will be useful when working with null pointers or values requiring specific processing.
- is_integral<T>: This function lets us determine whether a given type T, such as int, char, or bool, is an integral type. It is practical for handling the many behaviors connected to integer-type behaviors.
- is_floating_point<T>: Determines whether a type T is a floating-point type, such as a float or double. When you must particularly work with floating-point values, it is useful.
- is_array<T>: This function determines whether or not a type T is an array type. This function can let you differentiate between arrays and other kinds for specialized handling needs.
- is_enum<T>: It is used to determine whether a specific type T is an enumeration type. This method comes in helpful as a tool to assist us when we want to modify how these named values behave.
- is_union<T>: The function is_union<T> determines whether the given type T is a union type. This function can be utilized to handle unions uniquely from other kinds.
- is_class<T>: When determining whether a given type is a class or struct, the function is_class<T> can be useful. When you wish to apply certain logic or actions to classes or structs, a technique known as template metaprogramming comes in handy.
- is_function<T>: Checks whether the type T is a function type. This function is helpful when you must differentiate between functions and other types.
- is_pointer<T>: Determines whether the type T is a pointer type using is_pointer<T>. The behavior of pointer types can be modified with this.
- is_lvalue_reference<T>: It is used to determine whether a specific type exists. A reference of the type T points to a particular location in memory (typically indicated by a lvalue reference, such as T&). This function is particularly helpful for working with reference-related notions in various ways.
- is_rvalue_reference<T>: Checks whether a type T is an rvalue reference type (T&&) using the is_rvalue_referenceT> function. To manage rvalue references individually, this can be utilized.
- is_member_object_pointer<T>: The function is_member_object_pointerT> determines whether a pointer of type T points to a non-static data member. Useful when working with pointers to variables belonging to classes.
- is_member_function_pointer<T>: Determines whether a type T is a pointer to a member function. Managing pointers to member functions is useful.
- is_member_pointer<T>: This characteristic combines the first two. The type T's status as a pointer to either a member object or member function is determined by this property.
Example of primary type traits:
#include <iostream>
#include <type_traits>
using namespace std;
enum Color { RED, GREEN, BLUE }; // Define the enumeration
// Template function that prints information about a type using primary type traits
template <typename T>
void sample() {
cout << "Type: " << typeid(T).name() << endl;
cout << "Is an integer type: " << (is_integral<T>::value ? "Yes" : "No") << endl;
cout << "Is a floating point type: " << (is_floating_point<T>::value ? "Yes" : "No") << endl;
cout << "Is an array type: " << (is_array<T>::value ? "Yes" : "No") << endl;
cout << "Is an enumeration type: " << (is_enum<T>::value ? "Yes" : "No") << endl;
cout << "Is a pointer type: " << (is_pointer<T>::value ? "Yes" : "No") << endl;
cout << "Is an lvalue reference type: " << (is_lvalue_reference<T>::value ? "Yes" : "No") << endl;
cout << "Is an rvalue reference type: " << (is_rvalue_reference<T>::value ? "Yes" : "No") << endl;
}
int main() {
// Call the sample() function with different types to demonstrate the usage of primary-type traits
sample<int>();
sample<double>();
sample<int[]>();
sample<Color>(); // Use the enumeration type here
sample<int*>();
sample<int&>();
sample<int&&>();
return 0;
}
Output:
![C++ Type Traits](https://static.tutorialandexample.com/cpp/cpp-type-traits1.png)
Similarly, for all types of traits, it will be displayed.
The above program is an example of how to use main type traits in C++.
Explanation: The code includes the required header files for utilizing the capability of type characteristics and the standard input/output stream, respectively.
- An inventory Color is defined as the representation of many colors.
- The template method sample () accepts a type T as a template parameter.
- First, it enters the main () function. It executes the sample () function with various types to show how primary traits are used.
When the program is run, it will produce details about each type, including its name and whether it is an integral, floating-point, array, enumeration, pointer, lvalue reference, or rvalue reference.
Composite Type Traits
Multifaceted personality qualities called composite-type attributes combine different underlying traits. They encompass a variety of features as opposed to single traits, providing a more comprehensive explanation of behavior.
- The function is_fundamental<T> determines whether the type T (integral, floating-point, or void) is a fundamental type.
- is_arithmetic<T>: We can determine whether the type T is an arithmetic type (integral or floating-point) using the is_arithmetic<T> function.
- The function is_scalar<T> determines whether the type T (arithmetic, enumeration, pointer, or member pointer) is a scalar type.
- Checks whether a type T is an object type (anything other than functions, references, or void) using the is_object<T> function.
- Check whether the type T is a compound type (anything other than fundamental or reference types) using the is_compound<T> function.
- Tests whether the type T is a reference type using the is_reference<T> function.
- Check whether the type T is a member pointer using the is_member_pointer<T> function.
Example for composite type traits:
#include <iostream>
#include <type_traits>
using namespace std;
// Define a simple class and an enumeration
class MyClass {};
enum Color { RED, GREEN, BLUE };
int main() {
// Print a header for the demo
cout << "Composite Type Traits Demo" << std::endl;
// Use type traits to check properties of the MyClass type
cout << "is_fundamental<MyClass>: " << is_fundamental<MyClass>::value << endl;
cout << "is_arithmetic<MyClass>: " << is_arithmetic<MyClass>::value << endl;
cout << "is_scalar<MyClass>: " << is_scalar<MyClass>::value <<endl;
cout << "is_object<MyClass>: " << is_object<MyClass>::value << endl;
cout << "is_compound<MyClass>: " << is_compound<MyClass>::value << endl;
cout << "is_reference<MyClass>: " << is_reference<MyClass>::value << endl;
cout << "is_member_pointer<MyClass>: " << is_member_pointer<MyClass>::value << endl;
return 0;
}
Output:
![C++ Type Traits](https://static.tutorialandexample.com/cpp/cpp-type-traits2.png)
Type Property Queries
- is_const<T> determines whether T is a type that qualifies as const.
- is_volatile<T> determines whether T is a type that qualifies as volatile.
- It can be copied by memcpy if T is a trivial type, according to the is_trivial<T> function.
- The function is_standard_layout<T> determines whether T has a standard layout (meets certain memory layout specifications).
- The method is_polymorphic<T> determines whether the type T is polymorphic (has at least one virtual function).
- If T is an abstract class type (has only virtual functions), it can be determined using the is_abstract<T> method.
- The function is_signed<T> checks whether T is a signed arithmetic type.
Example:
//We include necessary libraries for input/output and type traits.
#include <iostream>
#include <type_traits>
// We're using the standard namespace for easier access to standard features.
using namespace std;
// Let's define a class that we'll use to demonstrate type properties.
class TypeProperty {
// We're adding a virtual " sample " function to make this class polymorphic.
virtual void sample() {}
};
// The main function where our program starts executing.
int main() {
// We're printing a header to introduce the type property queries demonstration.
cout << "Type Property Queries Demo" << endl;
// Now, let's check some properties of different types.
// We're checking if the type "int" is const and volatile.
cout << "Is int const?: " << is_const<int>::value << endl;
cout << "Is int volatile?: " << is_volatile<int>::value << endl;
// We're checking if the type "int" is trivial.
cout << "Is int trivial?: " << is_trivial<int>::value << endl;
// We're checking if the type "int" has a standard memory layout.
cout << "Is int standard layout?: " << is_standard_layout<int>::value << endl;
// We're checking if the class "TypeProperty" is polymorphic (contains at least one virtual function).
cout << "Is TypeProperty polymorphic?: " << is_polymorphic<TypeProperty>::value << endl;
// We're checking if the class "TypeProperty" is an abstract class (contains only virtual functions).
cout << "Is TypeProperty abstract?: " << is_abstract<TypeProperty>::value << endl;
// We're checking if the type "int" is a signed integer type.
cout << "Is int signed?: " << is_signed<int>::value << endl;
// We're done with our demonstrations.
return 0;
}
Output:
![C++ Type Traits](https://static.tutorialandexample.com/cpp/cpp-type-traits3.png)
Type Relationships Traits
- is_same<T, U> This characteristic evaluates the similarity of the two types, T and U. Based on type equality, it allows or turns off template specializations.
- is_base_of <Base, Derived>: This property determines whether Derived is privately or openly descended from Base. It is frequently used to implement polymorphism or inheritance-related behavior.
- is_convertible<T, U>: If an object of type T can be implicitly transformed to type U, it depends on this trait. When handling type conversions or overload resolution, it is helpful.
Example for type relationship trait:
#include <iostream>
#include <type_traits>
class Parent {};
class Child: public Parent {};
using namespace std;
int main() {
cout << "Type Relationship Traits Demo" << endl;
// Check if the two types are the same
cout << "Is int the same as int?: " << is_same<int, int>::value << endl;
cout << "Is int the same as double?: " << is_same<int, double>::value << endl;
// Check if one type is a base class of another
cout << "Is Parent a base class of Child?: " << is_base_of<Parent, Child>::value << endl;
cout << "Is Child a base class of Parent?: " << is_base_of<Child, Parent>::value << endl;
// Check if a type is convertible to another
cout << "Is int convertible to double?: " << is_convertible<int, double>::value << endl;
cout << "Is double convertible to int?: " << is_convertible<double, int>::value << endl;
return 0;
}
Output:
![C++ Type Traits](https://static.tutorialandexample.com/cpp/cpp-type-traits4.png)
Type Transformation Traits:
- add_const<T> and remove_const<T>: These characteristics modify type T by adding or removing the const qualifier. They are employed to change the characteristics of types, such as when a non-const version of a type is required.
- add_lvalue_reference, add_rvalue_reference, remove_reference<T> These characteristics alter type T by adding or removing reference qualifiers. They support working with transformations involving references.
- add_pointer<T> and remove_pointer<T>: These characteristics modify type T by adding or removing a pointer qualifier. They come in handy when you need to work with or alter pointers.
- The type T would change if submitted as a value to a function provided by the trait decay<T>. References, const qualifiers, and decaying array types are all removed with it.
Example:
#include <iostream>
#include <type_traits>
using namespace std;
int main() {
cout << "Type Transformation Traits Demo" << endl;
// Adding and removing const qualifiers
using T1 = add_const<int>::type;
using T2 = remove_const<const int>::type;
cout << "add_const<int>: " << is_same<T1, const int>::value << endl;
cout << "remove_const<const int>: " << is_same<T2, int>::value << endl;
// Adding and removing references
using T3 = add_lvalue_reference<int>::type;
using T4 = add_rvalue_reference<int>::type;
using T5 = remove_reference<int&>::type;
cout << "add_lvalue_reference<int>: " << is_same<T3, int&>::value << endl;
cout << "add_rvalue_reference<int>: " << is_same<T4, int&&>::value << endl;
cout << "remove_reference<int&>: " << is_same<T5, int>::value << endl;
// Adding and removing pointers
using T6 = add_pointer<int>::type;
using T7 = remove_pointer<int*>::type;
cout << "add_pointer<int>: " << is_same<T6, int*>::value << endl;
cout << "remove_pointer<int*>: " << is_same<T7, int>::value << endl;
// Decay trait
using T8 = decay<const volatile int&>::type;
cout << "decay<const volatile int&>: " << is_same<T8, int>::value << endl;
return 0;
}
Output:
![C++ Type Traits](https://static.tutorialandexample.com/cpp/cpp-type-traits5.png)
Advantages of Type Traits in C++
- Compile time checking: Type traits enable you to make judgments and perform checks at compile time rather than runtime. Removing pointless runtime tests can detect issues early in development and improve speed.
- Code readability: By explicitly declaring the type attributes and relationships, type traits make your code more self-explanatory and simpler to understand. which could enhance collaboration and maintenance.
- Template Metaprogramming: Type traits are essential for template metaprogramming, which enables you to create code that manipulates types as though they were values. Code that is highly generic and reusable is produced in this way.
- Generic programming: Type traits allow you to create generic code that can adapt to many kinds without repeating logic. This generic encourages code reuse and cuts down on duplication.
- Error Prevention: Type traits offer a standardized approach to query type data and properties, which helps prevent errors. This error prevention technique reduces the likelihood of using incompatible types or assuming the wrong types.
- Type compatibility: Type attributes make type conversions and checks for compatibility easier. Runtime errors can be prevented by verifying compatible types before performing operations.
- Enhanced Documentation: By utilizing type characteristics, you can directly document type requirements and constraints in the code, making it simpler for other developers to comprehend how to properly utilize your methods and classes.
- Support for IDEs: Using type traits, many integrated development environments (IDEs) can offer better code completions and suggestions, resulting in higher productivity.
Conclusion
C++ type traits allow programmers to simultaneously examine and work with types. They allow you to ascertain the core characteristics of types, alter them, and examine their interrelationships.
By employing type traits, you can write more adaptable, effective, and error-proof code. They improve the functionality of C++ and make it possible to employ more sophisticated coding approaches. They are especially helpful in template metaprogramming and generic programming.