Passing Lambda Functions in C: A Comprehensive Guide

Introduction

In the realm of C programming, lambda functions are a powerful tool that allows for more functional and dynamic code. Lambda functions, also known as anonymous functions that can capture variables from their surrounding scope, can be passed as arguments to other functions. This article is a comprehensive guide on how to pass lambda functions in C, along with key points and an illustrative example.

Basic Syntax

The syntax for defining a lambda function is as follows:

n [captures]parameters - return_type { body }

Defining a Lambda Function

A lambda function is defined using the lambda operator []. It can have a capture list, parameters, and a body. Here is the general syntax:

Passing the Lambda

You can pass a lambda to a function that takes a function pointer or a callable object. This is typically done by wrapping the lambda in std::functionreturn_type(parameters).

Here’s a simple example illustrating how to pass a lambda function to another function:

void applyFunction(const std::vectorint vec, const std::functionvoid(int) func) {    for (int num : vec) {        func(num);    }}

In the example, the function applyFunction takes a vector of integers and a callable object func, which is a lambda in this case.

Example: Passing Lambda in C

Include iostreamInclude vectorInclude algorithmvoid applyFunction(const std::vectorint vec, const std::functionvoid(int) func) {    for (int num : vec) {        func(num);    }}int main() {    std::vectorint numbers  {1, 2, 3, 4, 5};    // Define a lambda function    auto print  [](int n) {        std::cout  n  std::endl;    };    // Pass the lambda to the function    applyFunction(numbers, print);    std::cout  std::endl;    // You can also pass a lambda directly    applyFunction(numbers, [](int n) {        std::cout  n  " * "  n  std::endl;    });    return 0;}

In this example, the lambda functions print the number and the square of the number.

Key Points

Capturing Variables

The capture list allows you to capture variables from the surrounding scope. For example:

int x  10;auto lambda  [x](int n) { return x   n };

This lambda captures the variable x by value.

Using std::function

The std::function type is used to store the lambda, allowing you to pass it to functions. This header must be included to use std::function.

Compile with C11 or Later

To use lambdas in C, compile your code with C11 or later standard. They were introduced in C11.

Conclusion

Passing lambda functions in C is a powerful technique that enables more dynamic and functional code. By understanding and utilizing lambda functions, you can create more flexible and reusable code structures.

Further Reading

For more information on using lambda functions in C, you may want to explore the std::function documentation.