Standard concepts
- C++ course
- Advanced
- Lesson 63/83
- 5 min
Learn standard concepts (Integral, FloatingPoint).
Standard concepts
C++20 ships frequently used concepts in the <concepts> header. The best known are: std::integral, std::floating_point, std::signed_integral, std::unsigned_integral, std::convertible_to, std::same_as and std::copyable.
With them you do not have to write template constraints from scratch. Example: template<std::integral T> T sum(T a, T b). Here T accepts only integral types (int, long, char, ...). This short form means the same as requires std::integral<T>.
Integral and FloatingPoint
std::integral and std::floating_point are the two most used concepts in numeric code. When a template function should accept only integers or only floating-point values, you use these.
Example: template<std::floating_point T> T average(T a, T b) { return (a + b) / T{2}; }. Called with int this function fails to compile, because int is not a floating_point. So type errors are caught at compile time, not at runtime.
Practice Integral-constrained sum function
Write the template function template<std::integral T> T sum(T a, T b) with body return a + b;. In main call sum(3, 4) and print the result with std::cout.
Starter code
#include <iostream>
#include <concepts>
// Write the sum template function here
int main() {
// Print the result of the sum call
return 0;
}Sample solution
#include <iostream>
#include <concepts>
template<std::integral T>
T sum(T a, T b) {
return a + b;
}
int main() {
std::cout << sum(3, 4);
return 0;
}Expected output
7
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each concept to its description
| Term | Meaning |
|---|---|
std::integral |
Integer types |
std::floating_point |
Floating-point types |
std::same_as |
Same type assertion |
std::copyable |
Copyable type |
2 the std::integral constraint
template<____ T> T square(T x) { return x * x; }template<std::integral T> T square(T x) { return x * x; }Explanation: The std::integral constraint accepts only integer types.
3 Is std::integral<int> true?
- Yes, int is an integral type Correct answer
- Only for unsigned int
- No, int is not integral
- Only for long
Explanation: Types like int, long, char and short satisfy std::integral.