Pointer parameter passing vs reference parameter passing vs value parameter passing

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Preface

Have you ever encountered such a dilemma , Calling someone else's api when , Whether it's value transfer , The reference , Transmission pointer , It's easy to use , But I'm making it myself api when , But I got stuck here. I should adopt pointer to pass parameters , Value pass parameter or reference ？ This dilemma of uncertain choices .

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One 、 Pointer and reference are different

The pointer ： Pointer is also a variable , What is stored is the address of other variables , So a pointer accessing a variable is an indirect access . A pointer is an entity , Memory space needs to be allocated . Pointers don't have to be initialized when they are defined , And the space that points to is variable . Pointer self increment operation , The result pointer points to the next space .

quote ： References are just aliases for variables , There is no need to allocate memory space . Reference access to a variable is a direct access to . References must be initialized when they are defined , And it can't change . The underlying reference is implemented through pointers ; Quote autoincrement , The result is the quoted variable value plus 1

It's also different as a parameter , The essence of passing a pointer is to pass a value , The value passed is the address of the pointer ; The essence of transmission reference is address , Passing the address of the variable , So when should I pass the pointer , When will it be transmitted and quoted ？

Two 、 For functions that do not modify the incoming parameters

1. If the data object is small , Such as built-in data types or small structures , Is passed by value ;
2. If the data object is an array , Then use the pointer （ The only choice ）, And the pointer is declared as pointing const The pointer to ;
3. If the data object is a large structure , Then use const Pointer or reference , The efficiency of the procedure has been improved . This can save the time and space required by the structure ;
4. If the data object is a class object , Then use const quote （ The standard way to pass class object parameters is by reference ）;

3、 ... and 、 For functions that modify incoming parameters

1、 If the data is a built-in data type , Then use the pointer
2、 If the data object is an array , Only pointers can be used
3、 If the data object is a structure , Use a reference or pointer
4、 If the data is a class object , Use reference

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One last word ： Pointer is not type safe ( There are more references than pointers, type checking ） It's best to do type checking before using pointers , Prevent the appearance of wild pointer ;