Modern C++ and C Alternatives

C++ Lambdas and C Closures

A lambda creates an unnamed callable object and may capture local state; C callbacks need context passed explicitly.

What is C++ Lambdas and C Closures?

A lambda creates an unnamed callable object and may capture local state; C callbacks need context passed explicitly.

Capture context for a callback.

Important points

Understand the C mechanism before comparing the C++ abstraction.
Use RAII and value semantics to express ownership.
Prefer type-safe compile-time abstractions over macros and casts.

C and C++ code examples

Run code →

main.c

#include <stdio.h>

int above(int value, void *context) {
    return value > *(int *)context;
}

int main(void) {
    int values[] = {2, 7, 4, 9};
    int threshold = 5;
    int count = 0;
    for (int index = 0; index < 4; ++index) {
        count += above(values[index], &threshold);
    }
    printf("%d\n", count);
}

Expected output

C++

Run code →

main.cpp

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

int main() {
    std::vector values{2, 7, 4, 9};
    int threshold = 5;
    auto above = [threshold](int value) {
        return value > threshold;
    };
    std::cout << std::count_if(values.begin(), values.end(), above)
              << '\n';
}

Expected output

C and C++ comparison

The C function receives a void pointer and casts it to known context. The C++ lambda captures threshold by value, keeping type information without manual casting.

C uses naming conventions, callbacks, macros, and explicit context structures.

C++

Language features provide scoped, type-safe, and often zero-overhead abstractions.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Write the C mechanism before the C++ abstraction.
Remove manual cleanup with RAII.
Check whether the abstraction adds allocations or virtual dispatch.