How to Check If All Elements in a Range Satisfy a Specific Condition in C++

To check if all elements in a range satisfy a specific condition in C++, you can use the std::all_of() algorithm from the <algorithm> header.

This function returns true if the provided predicate is satisfied by all elements in the range [first, last), and false otherwise.

Here’s an example:

1#include <vector>
2#include <algorithm>
3#include <iostream>
4
5int main() {
6  std::vector<int> numbers {2, 4, 6, 8, 10};
7
8  bool all_even = std::all_of(
9    numbers.begin(), numbers.end(), [](int num) {
10      return num % 2 == 0;
11    }
12  );
13
14  if (all_even) {
15    std::cout << "All numbers are even.";
16  } else {
17    std::cout << "Not all numbers are even.";
18  }
19}

1All numbers are even.

How It Works

• Including the Header: Include the <algorithm> header to access the std::all_of() function.
• Using std::all_of(): This function takes three parameters: the beginning and end of the range, and a unary predicate that returns true for elements that satisfy the condition and false otherwise.

Practical Uses

• Validation: std::all_of() is commonly used to validate that all elements in a container meet a certain criterion, such as checking if all numbers are positive, all strings are non-empty, or all objects in a collection have a specific property.
• Early Exit: std::all_of() stops processing as soon as it finds an element that does not satisfy the predicate, making it efficient for large datasets where early exit can save processing time.

Example: Checking Custom Conditions

You can check any custom condition by providing the appropriate lambda function or functor. Here’s an example checking if all elements are greater than a certain value:

1#include <algorithm>
2#include <iostream>
3#include <vector>
4
5int main() {
6  std::vector<int> numbers{5, 7, 9, 11};
7
8  bool all_greater_than_five = std::all_of(
9    numbers.begin(), numbers.end(), [](int num) {
10      return num > 5;
11    }
12  );
13
14  if (all_greater_than_five) {
15    std::cout
16      << "All numbers are greater than five.";
17  } else {
18    std::cout
19      << "Not all numbers are greater than five.";
20  }
21}

1Not all numbers are greater than five.

Conclusion

The std::all_of() algorithm is a powerful tool for validating ranges of elements against specific conditions. It simplifies the code and enhances readability while providing efficient performance.

Whether you are validating user input, processing data, or implementing business rules, std::all_of() can be a valuable addition to your toolkit.