ISR Callback Alias

Question

Problem: ISR Callback Alias. Solve this hands-on electronics task on EWskills.

Accepted Answer

#include 
#include 

using namespace std;

// Alias for a function pointer that returns void and takes an int32_t
using ISRCallback = void (*)(int32_t);

void onError(int32_t code) {
    cout << "ERROR " << code;
}

void onComplete(int32_t code) {
    cout << "COMPLETE " << code;
}

int main() {
    int32_t mode, eventCode;
    if (!(cin >> mode >> eventCode)) return 0;

    // Declare the callback variable using the alias
    ISRCallback cb = nullptr;

    // Select callback based on mode
    if (mode == 1) {
        cb = onError;
    } else if (mode == 2) {
        cb = onComplete;
    }

    // Invoke through the function pointer
    if (cb) {
        cb(eventCode);
    }

    return 0;
}

Explanation & Logic Summary:

Type Aliasing
using ISRCallback = void (*)(int32_t); creates a readable and reusable alias for a function pointer type, preferred over typedef in modern C++.
Decoupling
The main logic does not depend on the implementation details of the callbacks, only on their interface.
Safety
Initializing the function pointer to nullptr and checking before invocation prevents undefined behavior, which is critical in firmware systems.

Firmware Relevance & Real Embedded Meaning:

ISR-to-Application Communication
This pattern is widely used in HALs and drivers to notify application code of hardware events without tight coupling.
Efficiency
Function pointers provide deterministic and low-overhead dispatch compared to virtual functions, making them suitable for ISR-related paths.
Practical Skill
Understanding and safely using function pointers is a foundational Embedded C++ skill for real-world firmware development.

53. ISR Callback Alias