Follow the article if you want a detailed explanation of how the callback function works.
What Is a Callback Function
A callback in C is a function passed as an argument to another, higher-level function. This allows the higher-level function to call the lower-level, callback function at the appropriate time. This is useful in creating programs with complex behavior, as it allows you to break the complex behavior down into small, reusable pieces. As a result, simpler code is produced that is simpler to comprehend, maintain, and test.
When developing drivers or custom libraries, callback functions are a fundamental and frequently crucial notion that developers must understand. A callback function provides a reference to executable code that is sent as an argument to other code, allowing a lower-level software layer to execute a function specified in a higher-level one. Using a callback, a driver or library developer can define a behavior at a lower layer while leaving the application layer to define the implementation.
Callbacks are commonly used in programming language designs and libraries, such as object-oriented programming, event-driven programming, and GUI programming. They are also used in embedded systems programming and even application programming interface (API) design.
A callback function is only a function pointer that is sent as a parameter to another function at the most fundamental level. A callback typically consists of three parts: Callback execution, Callback registration, and the callback function.
Advantages of Callback Functions
Utilizing callbacks has the primary benefit of allowing subroutines written at lower software levels to call functions created at higher software levels. You can also use a callback for signals or alerts.
How to Implement a Callback Function?
In C, you can implement callbacks using function pointers. To refer to a function specified elsewhere in the program, function pointers are employed. When the higher-level function needs to call the callback function, it does so by dereferencing the function pointer to get back the address of the callback function. It then uses this address as the argument for the call.
void A()
{
printf("This is an article on Callbacks\n");
}
void Callback(void (*ptr)())
{
(*ptr) ();
}
int main()
{
void (*ptr)() = &A;
Callback(ptr);
return 0;
}
In this code, we are creating two functions; a normal function (A()) and a callback function (callback()). And in the main() function, we are calling the function A() using the callback() function which prints the output.
Output
Final Thoughts
Callbacks in C are important functions that help users in creating programs with more complex behavior. By allowing the lower-level functions to be called when needed, callbacks enable the program to break down complex behavior into small, reusable pieces. This makes it simpler to maintain and troubleshoot the code. With the use of function pointers and function objects, you can use callback to provide dynamic, state-dependent behavior for the program.
