Pointers and reference parameters in function declarations: dissecting their usage and semantics

Pointer parameters allow functions to access and modify the original data, while reference parameters must be bound to a valid variable, and changes to the reference are also reflected on the original value.

Pointer and reference parameters in function declarations: a deeper understanding of their usage and semantics

Pointer parameters

Pointer parameters allow functions to access and Modify the caller's original data. Pointer parameters are usually declared as pointers to target types T, as follows:

void modify_value(int* num);

This function declaration indicates that the modify_value function takes a pointer to an integer as a parameter. The integer is accessible to the argument passed to this function, and any changes to the pointed-to value are reflected in the caller's original value.

Practical case:

int main() {
  int num = 10;
  modify_value(&num); // 传递 num 的地址
  cout << num << endl;  // 输出 20，因为原始值已修改
  return 0;
}

void modify_value(int* num) {
  *num = *num * 2; // 修改指向的值
}

Reference parameters

Reference parameters are also references to the target type, but they are conceptually different. Reference parameters are represented in the declaration as a reference (&) to the target type, as follows:

void modify_value(int& num);

modify_value The function takes a reference to an integer as a parameter. The argument passed to this function must be a valid integer variable, and any changes to the reference variable are reflected in the caller's original variable.

It should be noted that reference parameters cannot be rebind to different variables, which means that the value passed to the reference parameter must be the entire lifetime of the function.

Practical case:

int main() {
  int num = 10;
  modify_value(num); // 传递 num 的引用
  cout << num << endl;  // 输出 20，因为原始值已修改
  return 0;
}

void modify_value(int& num) {
  num = num * 2; // 修改引用变量
}

The difference between pointers and references

Although both pointers and references can access and modify the caller's original data, But there are some key differences between them:

• Directivity:A pointer can point to any valid memory location, while a reference must be bound to a valid variable.
• Rebindable: Pointers can be rebinded to different memory locations, while references cannot be rebinded.
• Overhead: Usually pointers consume more overhead than references because they need to store the address pointing to the target location.

Conclusion

Pointer and reference parameters are useful mechanisms in C for passing and modifying data between functions. Understanding their usage and semantics is crucial to writing code effectively.

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