用C交换指针 [英] Swapping pointer in C

问题描述

 ＃包括LT＆;＆stdio.h中GT;
无效之谜（INT * PTRA，为int *的ptrB）{
     INT *温度;
     TEMP =的ptrB;
     的ptrB =成形术;
     PTRA =温度;
}
诠释主（）{
    诠释一个= 2016年，B = 0，C = 4，D = 42;
    谜（安培;一，和b）;
    如果（一个c为C）
          谜（和C，和放大器;一个）;
    谜（安培;一，和D）;
    打印F（％d个\\ N，一）;
}
 

---

我尝试：

A和D是不交换的功能之谜（）不会改变值，但三分球这是本地的功能。

  

你能在正式的方式解释，请。如何运作功能之谜？

解决方案

  

A和D是不交换的功能之谜（）不会改变值，但三分球这是本地的功能。

是的，你是对的。功能之谜不交换值。它只是换指针 PTRA 和的ptrB 由的ptrB PTRA 分别为$ C>和。

  A
                 + -------------- +
                 | |
PTRA ----------＆GT; | 2016年|
                 | |
                 + -------------- +                        b
                 + -------------- +
                 | |
----------的ptrB GT＆; | 0 |
                 | |
                 + -------------- +
 

执行语句后

  TEMP =的ptrB;
的ptrB =成形术;
PTRA =温度;                        一个
                 + -------------- +
                 | |
PTRA ----- + | 2016年|
        + ------＆GT; | |
        | | + -------------- +
        | |
        | |
        | |
        | | b
        | | + -------------- +
        | | | |
---的ptrB + ----＆GT; | 0 |
                 | |
                 + -------------- +
 

# include <stdio.h>
void mystery (int *ptra, int *ptrb) {  
     int *temp; 
     temp = ptrb;  
     ptrb =ptra; 
     ptra = temp; 
} 
int main () { 
    int a = 2016, b=0, c= 4, d = 42; 
    mystery (&a, &b);
    if (a < c) 
          mystery (&c, &a); 
    mystery (&a, &d); 
    print f("%d\n", a); 
}

---

My attempt :

a and d are not swapped as the function mystery() doesn’t change values, but pointers which are local to the function.

Can you explain in formal way, please. how works function mystery?

解决方案

a and d are not swapped as the function mystery() doesn’t change values, but pointers which are local to the function.

Yes, you are right. Function mystery is not swapping values. It is just swapping the pointer ptra and ptrb to location pointed by ptrb and ptra respectively.

                        a
                 +--------------+
                 |              |
ptra ----------> |    2016      |
                 |              |
                 +--------------+



                        b
                 +--------------+
                 |              |
ptrb ----------> |      0       |
                 |              |
                 +--------------+

After executing statements

temp = ptrb;  
ptrb =ptra; 
ptra = temp;    

                        a
                 +--------------+
                 |              |
ptra -----+      |    2016      |
        +------> |              |
        | |      +--------------+
        | |
        | |
        | |
        | |             b
        | |      +--------------+
        | |      |              |
ptrb ---+ +----> |      0       |
                 |              |
                 +--------------+

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