C std::is_same example
std::is_same is used to determine whether the two types are exactly the same at compile time and return a bool value. 1. In the basic usage, std::is_same
std::is_same
is a type trait provided by the <type_traits></type_traits>
header file in the C standard library, which is used to determine whether the two types are exactly the same at compile time. It returns a bool
value, accessing the result via ::value
.

Here is a clear example of using std::is_same
:
Basic usage examples
#include <iostream> #include <type_traits> int main() { std::cout << std::boolalpha; // output true/false instead of 1/0 //Judge basic type std::cout << "int and int: " << std::is_same<int, int>::value << '\n'; // true std::cout << "int and const int: " << std::is_same<int, const int>::value << '\n'; // false std::cout << "int and int&: " << std::is_same<int, int&>::value << '\n'; // false std::cout << "int and int&&: " << std::is_same<int, int&&>::value << '\n'; // false std::cout << "int and double: " << std::is_same<int, double>::value << '\n'; // false // Pointer type std::cout << "int* and int*: " << std::is_same<int*, int*>::value << '\n'; // true std::cout << "int* and const int*: " << std::is_same<int*, const int*>::value << '\n'; // false // Reference type std::cout << "int& and int&: " << std::is_same<int&, int&>::value << '\n'; // true // Use remove_const to compare std::cout << "remove_const_t<const int> and int: " << std::is_same<std::remove_const_t<const int>, int>::value << '\n'; // true // Use remove_reference to remove reference std::cout << "remove_reference_t<int&> and int: " << std::is_same<std::remove_reference_t<int&>, int>::value << '\n'; // true return 0; }
Output result:
int and int: true int and const int: false int and int&: false int and int&&: false int and double: false int* and int*: true int* and const int*: false int& and int&: true remove_const_t<const int> and int: true remove_reference_t<int&> and int: true
Practical application scenarios
std::is_same
is often used in template metaprogramming, such as:

- Conditional compilation logic (with
if constexpr
) - Overload or specialized templates
- Type Safety Check
Example: Different logic is executed according to the type in the function template
#include <iostream> #include <type_traits> #include <string> template<typename T> void printType(const T& value) { if constexpr (std::is_same_v<T, int>) { std::cout << "Integer: " << value << '\n'; } else if constexpr (std::is_same_v<T, double>) { std::cout << "Double: " << value << '\n'; } else if constexpr (std::is_same_v<T, std::string>) { std::cout << "String: " << value << '\n'; } else { std::cout << "Unknown type\n"; } } int main() { printType(42); // Integer printType(3.14); // Double printType(std::string{"Hello"}); // String return 0; }
? Note: From C 17,
std::is_same_v<t u></t>
can be used as the abbreviation ofstd::is_same<t u>::value</t>
.
Basically that's it. std::is_same
is one of the cornerstones of type judgment, and it is very flexible to use with other type traits.

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