How to use C++ reference and pointer parameter passing?

References and pointers in C are both methods of passing function parameters, but there are differences. A reference is an alias for a variable. Modifying the reference will modify the original variable, while the pointer stores the address of the variable. Modifying the pointer value will not modify the original variable. When choosing to use a reference or a pointer, you need to consider factors such as whether the original variable needs to be modified, whether a null value needs to be passed, and performance considerations.

Reference and Pointer Parameter Passing Guide in C

In C, references and pointers are two powerful tools for passing function parameters. They provide a way to modify variables in the calling function within a function.

References

A reference is a C data type that provides an alias to another variable. Once a reference is created, any modifications to it are reflected in the original variable.

Syntax:

Type& reference_variable = original_variable;

Example:

int x = 10;
int& ref_x = x;

ref_x++; // 等同于 x++
cout << x << endl;  // 输出：11

Pointers

Pointers are a C data type that stores the address of another variable. Primitive variables can be accessed by dereferencing pointers.

Grammar:

Type* pointer_variable = &original_variable;

Example:

int y = 10;
int* ptr_y = &y;

*ptr_y++; // 等同于 y++
cout << y << endl;  // 输出：11

Parameter difference

##Transmission methodReference valueAddress copyModification of the original variableModify the original variableYou can modify the original variable or addressAccess costLow (direct access)High (requires dereference)Memory allocation NoneAllocate dynamic memoryConstant referenceAvailableNot availablePass null valueNoOK

Features	Reference	Pointer

Practical case - value exchange in function

Use references to implement value exchange:

void swap_by_ref(int& a, int& b) {
  int temp = a;
  a = b;
  b = temp;
}

Use pointers to implement value exchange:

void swap_by_ptr(int* a, int* b) {
  int temp = *a;
  *a = *b;
  *b = temp;
}

Select the parameter passing method

Select references or pointers. When passing parameters, please consider the following factors:

• Whether the original variable needs to be modified:If necessary, use a reference.
• Whether a null value needs to be passed: If necessary, use a pointer.
• Performance considerations: If you need to access the original variable frequently, use references.

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