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Callback function is a very important and commonly used programming technique in C language, especially when dealing with event-driven or asynchronous programming. The following is a detailed analysis of callback function in C language:

1. What is a callback function?

A callback function is a function that is called through a function pointer. It allows a function to be passed as a parameter to another function and executed when a specific event occurs. This technique makes programming more flexible and can dynamically decide which function to call at which time.

2. Purpose of callback function

Callback functions are usually used in the following situations:

• Event Handling: When a specific event occurs, the system calls the registered callback function to handle the event.
• Asynchronous task completion notification: When the asynchronous task is completed, the main program is notified through the callback function.
• Timers and signal processing: When the timer expires or a signal occurs, the registered callback function is called.
• Data structure operations: For example, the comparison function in the sorting algorithm can dynamically determine the sorting rules through the callback function.

3. Basic implementation of callback function

In C, the implementation of a callback function usually involves the following steps:

3.1 Define callback function type

First, define the type of the callback function, usually implemented through a function pointer:

// 定义回调函数类型
typedef void (*CallbackType)(int);
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hereCallbackTypeIs a function pointer type that points to a function that has no return value and accepts aintFunctions of type parameters.

3.2 Registering callback function

In the main program, register the specific function as a callback function to the function that needs to be called:

// 函数接受回调函数作为参数
void performOperation(int data, CallbackType callback) {
    // 执行操作
    printf("Performing operation with data: %dn", data);
    
    // 调用回调函数
    callback(data);
}
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In this example,performOperationThe function accepts an integerdataand a callback functioncallbackAs a parameter. After it performs some operation, it calls the registered callback function to process the result.

3.3 Using callback functions

In the callperformOperation, pass a suitable function as the callback:

// 实现一个回调函数
void callbackFunction(int result) {
    printf("Callback function called with result: %dn", result);
}

int main() {
    // 注册回调函数
    performOperation(42, callbackFunction);
    
    return 0;
}
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In this example,mainIn the functioncallbackFunctionis registered as a callback function.performOperationWhen it completes its operation, it callscallbackFunctionand pass on the result.

4. Examples and Output

Here is the complete example code and output:

#include <stdio.h>

// 定义回调函数类型
typedef void (*CallbackType)(int);

// 函数接受回调函数作为参数
void performOperation(int data, CallbackType callback) {
    // 执行操作
    printf("Performing operation with data: %dn", data);
    
    // 调用回调函数
    callback(data);
}

// 实现一个回调函数
void callbackFunction(int result) {
    printf("Callback function called with result: %dn", result);
}

int main() {
    // 注册回调函数
    performOperation(42, callbackFunction);
    
    return 0;
}
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Output:

Performing operation with data: 42
Callback function called with result: 42
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5. Notes

• The registration and use of callback functions require attention to the consistency of function signatures, that is, the parameters and return value types of the callback function must match the requirements of the called function.
• When using dynamically allocated memory or a multi-threaded environment, pay attention to thread safety and memory management issues.

Through the above analysis, I hope you can better understand and apply the callback function technology in C language!

6. References

1. Kernighan, B. W., & Ritchie, D. M. (1988). The C Programming Language (2nd ed.). Prentice Hall.
2. Kerrisk, Michael. The Linux Programming Interface: A Linux and UNIX System Programming Handbook. No Starch Press, 2010.
3. ISO/IEC. (1999). ISO/IEC 9899:1999. Programming Languages – C.
4. ISO/IEC. (2024). ISO/IEC DIS 9899. Programming Languages – C.
5. Harbison, S. P., & Steele, G. L. (2002). C: A Reference Manual (5th ed.). Prentice Hall.
6. Prata, Stephen. C Primer Plus. Addison-Wesley Professional, 2013.

7. Conclusion

1. The contents of this section have been fully introduced. I hope that through this article, everyone will have a deeper understanding and knowledge of callback functions in C language.
2. Thank you for your reading and support. If you find this article helpful, please don’t hesitate to share yourLike and comment, which is very important to us. Thank you again for yourFollow and support！