What is the nature and working principle of C++ function pointers?

Function pointers are essentially variables that point to function memory addresses, allowing functions to be called dynamically at runtime. It contains the address pointing to the function, the function type, and pointer arithmetic capabilities. How it works involves getting the function address, pushing the parameters and return address, calling the function, and returning the return value and control to the calling code.

The essence and working principle of C function pointer

What is a function pointer?

A function pointer is a variable that points to the memory address of a function. It allows a program to dynamically call functions at runtime.

The essence of function pointers

• Type: The type of a function pointer is the same as the type of the function it points to.
• Value: The value of the function pointer is the memory address of the function.
• Pointer operations: Similar to other pointers, function pointers can perform pointer operations (addition, subtraction, comparison).

How function pointers work

When a function pointer is called, the compiler performs the following steps:

1. From the function Get the function address from the pointer.
2. Push parameters onto the stack.
3. Save the return address on the stack.
4. Call functions.
5. The return value is returned to the stack by the function.
6. Control returns to the calling code.

Sample code

The following code demonstrates how to create and use function pointers:

// 声明函数指针类型
typedef int (*FuncPtr)(int);

// 定义一个函数
int add(int a, int b) {
  return a + b;
}

int main() {
  // 创建一个指向 add 函数的函数指针
  FuncPtr ptr = &add;

  // 调用函数指针
  int result = ptr(3, 5);
  std::cout << "结果：" << result << std::endl;

  return 0;
}

Practical case

Function pointers are often used in the following scenarios:

• Callback function: Allows an object to register its own function as a callback to be called when a specific event is triggered.
• Dynamic loading: Functions can be loaded at runtime and called through function pointers.
• Object-oriented programming: Used to implement virtual functions, allowing subclasses to override parent class methods.

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