The relationship between C++ function parameter passing methods and dynamic memory allocation

In C, the function parameter passing method affects the function's processing and access of parameter data. Passing by value does not affect the actual parameters, while passing by reference and passing by pointer allow the function to modify the value of the actual parameter. Dynamic memory allocation allocates heap memory at runtime through the new and delete operators, and it is important to understand how this relates to how parameters are passed.

C The relationship between function parameter passing methods and dynamic memory allocation

In C, function parameters can be passed in the following three ways Passing:

• Passing by value: Pass a copy of the value of the actual parameter to the formal parameter. Changes to the actual parameter by the formal parameter will not affect the actual parameter.
• Pass by reference: Pass the reference of the actual parameter to the formal parameter. Changes to the actual parameter by the formal parameter will affect the actual parameter.
• Passing by pointer: Pass the pointer of the actual parameter to the formal parameter. The formal parameter can access and modify the actual parameter through the pointer.

Dynamic memory allocation refers to applying for memory space on the heap at runtime. It can use the new and delete operators to create and release objects.

It is important to understand the relationship between function parameter passing methods and dynamic memory allocation, because it affects how the function handles and accesses parameter data.

Practical case

Consider the following example:

#include <iostream>
using namespace std;

// 传值传递
void increment(int x) {
  x++;  // 对形参的改变不会影响实参
}

// 传引用传递
void increment_ref(int &x) {
  x++;  // 对形参的改变会影响实参
}

// 传指针传递
void increment_ptr(int *x) {
  *x++;  // 对形参的改变会影响实参
}

int main() {
  int a = 10;

  // 传值传递
  increment(a);
  cout << "After increment(a): " << a << endl;  // 输出 10

  // 传引用传递
  increment_ref(a);
  cout << "After increment_ref(a): " << a << endl;  // 输出 11

  // 传指针传递
  increment_ptr(&a);
  cout << "After increment_ptr(&a): " << a << endl;  // 输出 12

  return 0;
}

Conclusion

• Pass by value Does not affect the actual parameters, since it only copies the actual parameter values.
• Both passing by reference and passing by pointer allow functions to modify the values ​​of actual parameters.
• If the actual parameters need to be modified, this can be achieved by passing by reference or passing by pointer. If you only need to access the value of the actual parameter, you can use pass-by-value.
• When passing parameters through pointers, if you are not careful, problems such as dangling pointers may occur.

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