Impara Using Lambdas with STL Algorithms

Lambdas are a natural fit for use with the Standard Template Library (STL) algorithms in C++. Many STL algorithms, such as std::for_each, std::sort, and std::transform, require a function or callable object as a parameter to customize their behavior. Lambdas allow you to define these custom operations or predicates directly at the point of use, making your code concise and expressive. For example, you can use a lambda to print each element of a container, define a custom sorting rule, or transform data in a collection without writing separate function objects or named functions.

main.cpp


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#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
    std::vector<int> numbers = {1, 2, 3, 4, 5};

    // Use a lambda with std::for_each to print each element
    std::cout << "Original numbers: ";
    std::for_each(numbers.begin(), numbers.end(), [](int n) {
        std::cout << n << " ";
    });
    std::cout << std::endl;

    // Use std::transform with a lambda to square each element
    std::vector<int> squares(numbers.size());
    std::transform(numbers.begin(), numbers.end(), squares.begin(), [](int n) {
        return n * n;
    });

    std::cout << "Squared numbers: ";
    std::for_each(squares.begin(), squares.end(), [](int n) {
        std::cout << n << " ";
    });
    std::cout << std::endl;
}

Using lambdas directly with STL algorithms offers several advantages. You can define custom behavior exactly where it is needed, which keeps your code readable and eliminates the need for separate function definitions or functor classes. In the previous code, lambdas are used in-place to print elements and to transform each element by squaring it, illustrating how lambdas make your intent clear and your code more maintainable. This approach is especially helpful when the operation is simple or used only once, reducing boilerplate and keeping logic close to where data is processed.

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Sezione 3. Capitolo 1

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main.cpp


              123456789101112131415161718192021222324252627
            
#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
    std::vector<int> numbers = {1, 2, 3, 4, 5};

    // Use a lambda with std::for_each to print each element
    std::cout << "Original numbers: ";
    std::for_each(numbers.begin(), numbers.end(), [](int n) {
        std::cout << n << " ";
    });
    std::cout << std::endl;

    // Use std::transform with a lambda to square each element
    std::vector<int> squares(numbers.size());
    std::transform(numbers.begin(), numbers.end(), squares.begin(), [](int n) {
        return n * n;
    });

    std::cout << "Squared numbers: ";
    std::for_each(squares.begin(), squares.end(), [](int n) {
        std::cout << n << " ";
    });
    std::cout << std::endl;
}

Tutto è chiaro?

Grazie per i tuoi commenti!

Sezione 3. Capitolo 1