How to delete pointers correctly in golang

Golang is a very popular programming language because it has strong advantages in memory management. In Golang, we can use pointers to access the memory address of a variable and manipulate the variable through the pointer. However, when we deal with pointers, it is easy to have problems with memory leaks or "wild pointers". Therefore, this article will explain how to delete pointers correctly.

In Golang, using pointers allows us to access the memory address of variables more efficiently. However, if we don't manage pointers carefully, it can cause problems. For example, when we declare a pointer inside a function, the memory address pointed to by the pointer will only be released when the function ends. However, if this pointer is passed to other functions or persisted elsewhere, we need to delete the pointer manually.

The following is an example, assuming we have a Person structure:

type Person struct {
    Name string
}

func main() {
    p := &Person{Name: "Alice"}
    fmt.Println(p.Name)
}

In this example, we declare a Person structure pointer p and initialize it to a Person structure instance. We print the Name field of p, and then the program outputs "Alice". In this example, we do not need to delete p because p is declared in the main function and it will be automatically released when the function ends.

However, if we pass the pointer to other functions or persist it somewhere else, we must delete the pointer manually. If we do not delete the pointer, there will be a memory leak or "wild pointer" problem. Here is an example, assuming we declare a function f that receives a Person pointer and returns its Name field.

func f(p *Person) string {
    return p.Name
}

func main() {
    p := &Person{Name: "Alice"}
    fmt.Println(f(p))
}

In this example, we pass the address of p to function f, and then output its Name field. In this case, we don't have to remove p since it is declared in the main function and is just passed to another function. When function f ends, the memory address pointed to by p will be automatically released.

However, if we allocate a new Person structure in function f and return it to the caller, we must delete the pointer manually. Here is an example:

func createPerson(name string) *Person {
    return &Person{Name: name}
}

func main() {
    p := createPerson("Alice")
    fmt.Println(p.Name)
    // 在这里删除p指针
}

In this example, we declare a createPerson function that receives a string and returns a Person pointer. In the main function, we assign the return value of the function createPerson to p and print its Name field. In this example, you need to manually delete the p pointer because we allocate a new Person structure in the function createPerson and return its pointer. In the main function, we no longer need this pointer, so we need to delete it manually. We can use Golang's built-in function runtime.SetFinalizer to set up a function to be executed when the garbage collector collects the p pointer:

func finalizePerson(p *Person) {
    fmt.Printf("Deleting person with name %s\n", p.Name)
}

func createPerson(name string) *Person {
    p := &Person{Name: name}
    runtime.SetFinalizer(p, finalizePerson)
    return p
}

func main() {
    p := createPerson("Alice")
    fmt.Println(p.Name)
    // 在这里删除p指针
    runtime.GC() // 加入垃圾回收，用于验证指针已被删除
}

In this example, we declare a The function finalizePerson will print out the Name field of the Person structure that will be deleted. We use the runtime.SetFinalizer function in the function createPerson to set the finalizePerson function as the finalizer function of the p pointer. When Golang's garbage collector recycles the p pointer, the finalizePerson function will be automatically called. In the main function, we can use runtime.GC to force the garbage collector to run to verify that the p pointer has been deleted.

In short, the use of pointers is a key feature of the Golang programming language, which can improve the efficiency of the program. When using pointers, we must manage them carefully to avoid memory leaks or "wild pointer" problems. When deleting a pointer, we can use the runtime.SetFinalizer function to schedule a function to be executed during garbage collection.

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