The relationship between C++ function parameter passing methods and programming patterns

The function parameter passing method in C is closely related to the programming mode. Different passing methods will affect function behavior and mode selection. Passing variables by value is suitable for immutable objects or objects with high copy costs. Pass by reference to directly manipulate variables, suitable for input and output parameters, large objects and observer patterns. Passing by pointer allows handling of dynamic data structures and NULL pointers. When choosing a delivery method, you should consider object characteristics, functional operations, and programming patterns to achieve efficiency and design goals.

C The relationship between function parameter passing method and programming mode

In C, function parameters can be by value or by reference Or passed by pointer. Different delivery methods affect function behavior, memory usage, and programming pattern choices.

Transmission method

• Pass by value: The parameter copy is passed to the function, and the function operates on the copy value and will not affect the caller's variables .
• Pass by reference: Parameter reference is passed to the function, and the function directly operates the caller variable.
• Pass by pointer: The parameter pointer is passed to the function, and the function indirectly operates the caller variable through the pointer.

Programming Pattern

The transfer method is closely related to the programming pattern:

Pass by value:

• Immutable objects: If the function does not modify the object state, it is appropriate to use pass by value.
• Copy construction and assignment operations are expensive: If the cost of copying an object is high, pass by value should be avoided.

Pass by reference:

• Input and output parameters: Suitable for use when the function both returns results and modifies parameters. Pass by reference.
• Large objects: When the object is very large and the cost of copying is high, it can be passed by reference.
• Observer pattern: Observer functions should be passed by reference in order to observe changes in the object's state.

Pass by pointer:

• #NULL pointer: When a function accepts a pointer that may be NULL, it should be passed as Pointer passing.
• Dynamic data structures: Pointer passing allows functions to handle dynamically allocated data structures, such as linked lists and trees.

Practical case

Consider the following function, which exchanges two integers:

void swap_by_value(int a, int b)
{
  int tmp = a;
  a = b;
  b = tmp;
}

void swap_by_reference(int& a, int& b)
{
  int tmp = a;
  a = b;
  b = tmp;
}

Pass by value (swap_by_value)

• Copy transfer will not affect the caller's variables.
• Suitable for exchange operations on immutable objects (such as strings).

Pass by reference (swap_by_reference)

• Directly manipulate the caller variable.
• Suitable for exchange operations of mutable objects (such as integers).

Usage considerations

If two large integers are passed when calling the swap_by_value function, unnecessary copying will occur operate. Conversely, if you are passing an immutable string, passing by value is more efficient.

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