Introduction Implementing Callbacks in C is a powerful technique that allows you to pass functions as arguments to other functions. This capability gives your program the ability to respond dynamically to events, handle user-defined behavior, and promote modular code design. Instead of hardcoding specific logic, you can make your functions more flexible by accepting other functions as parameters and executing them based on runtime decisions. Why Study This Topic? Understanding Implementing Callbacks in C empowers you to build event-driven, modular, and flexible programs. Implementing Callbacks in C enables customization without changing base functionality—similar to how you might tell a delivery app to call you when your food arrives, instead of sending a generic message. Implementing Callbacks in C is especially important in real-time systems, device drivers, GUI frameworks, and even in custom sorting algorithms. For example, in an embedded system controlling smart lights, implementing callbacks in C can allow the user to define what happens when the motion sensor detects movement. What Will Be Covered? What is a callback? Syntax of function pointers How to implement callbacks in C Real-time examples and flow diagrams Interview questions and quizzes Practice coding exercises What is a Callback in C? A callback is a function passed as an argument to another function. This allows the called function to "call back" the passed-in function at a later point in its execution. Function Pointer Basics Before implementing a callback, you must understand function pointers. Here's the syntax: return_type (*pointer_name)(parameter_types); Example: void (*funcPtr)(int); You can now assign funcPtr to any function matching void func(int). Implementing a Simple Callback #include <stdio.h> void greet(int times) { for (int i = 0; i < times; i++) printf("Hello!\n"); } void executeCallback(void (*callback)(int), int n) { callback(n); // Call the passed-in function } int main() { executeCallback(greet, 3); return 0; } Output: Hello!Hello!Hello! Real-Time Example Imagine a smart alarm system. You want the user to define what happens when an intruder is detected: void callPolice() { printf("Calling the police...\n"); } void triggerAlarm(void (*action)()) { printf("Intruder detected!\n"); action(); // Callback } int main() { triggerAlarm(callPolice); return 0; } Summary A callback is a function passed as a parameter to another function. It requires knowledge of function pointers. Callbacks are useful for customization, event handling, and asynchronous behavior. They promote decoupled, reusable code. Learning Outcomes After this topic, learners will be able to: Declare and use function pointers in C Implement callback mechanisms Apply callbacks in real-world scenarios Build flexible and event-driven C programs Common Interview Questions Q1. What is a callback function in C?A: A function passed as an argument to another function.Asked in: TCS, Infosys Q2. How do you declare a function pointer in C?A: return_type (*pointer_name)(param_types);Asked in: Cognizant, Wipro Q3. Why are callbacks useful?A: They allow dynamic behavior and decouple implementation from action.Asked in: Capgemini, IBM Q4. Can you use callbacks for interrupt handling in embedded systems?A: Yes. They are ideal for such use cases.Asked in: Bosch, Honeywell Q5. What’s the difference between a function call and a callback?A: A function call is direct, whereas a callback is passed and invoked indirectly.Asked in: HCL, Accenture Practice Exercises Coding Task: Write a program that accepts a function pointer to display a greeting in different languages (English, Hindi, Tamil, etc.). Scenario You're building a music player. The app should notify the user when the next song is playing. Instead of hardcoding the action, you allow the user to pass a function—send a popup, play an animation, or log the song. This flexibility is exactly what callbacks enable in C. [quiz-cat id="21237"] Additional Resources Book: C Programming: A Modern Approach by K. N. King Article: Function Pointers in C Compiler: GCC IDE: Visual Studio Code, Code::Blocks
