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c - 变量上的地址没有改变

问题描述

我正在尝试使用变量的地址。但是，变量在每次运行时都具有相同的地址。既然我在不同的地址之间移动，为什么变量地址仍然相同？当我尝试复制结果时，它仍然给我相同的值。

typedef struct Node{
    char *color; /* Color of the light */
    int **details; /*holds the brightness and size*/
    struct Node* next;
}Node;

Node * light_info(char *filename){
    //Declaring two pointers so that the addresses are not lost while executing
    //the program 
    Node *tempNode = NULL;
    Node *tempHead = NULL;
    //Parameters
    FILE *fptr;
    int i =0;
    char fileInfo[MAXVALUE];
    fptr = fopen(filename,"r");
    if(fptr != NULL){
      while(fgets(fileInfo,sizeof(fileInfo),fptr)!= NULL){
           //Initalizing the value of token as NULL
            char * token = NULL;
            //Mallocs the space for the node 
            tempNode = malloc(sizeof(Node));
            //Check condition 
            if(tempNode == NULL){
                printf("Sorry cannot create a space on the heap;\n");
                perror("Error at line 61");
                exit(0);               
            }
            printf("NODE : %p \n",tempNode);
        // For the color
            token = strtok(fileInfo,",");
            char*  tempValue= malloc(50);
            tempValue = token;
            printf("%s \n",tempValue);
            printf("Temp value : %p \n",&tempValue);
            tempNode->color = tempValue;
        //Seprating 2 places for the details section 
            tempNode->details = malloc(sizeof(int)*2);
        //For the brightness
            token = strtok(NULL,",");
            int tempValueOfBrightness = atoi(token);
            printf("%p \n",&tempValueOfBrightness);
            printf("%d \n",tempValueOfBrightness);
            tempNode->details[0] = &tempValueOfBrightness;
        //For the size 
            token = strtok(NULL,"\n");
            int tempValueOfSize = atoi(token);
            printf("%d \n",tempValueOfSize);
                        printf("%p \n",&tempValueOfSize);
            tempNode->details[1] = &tempValueOfSize;
        //Adding the current address to the head to the node 
            tempNode->next = tempHead;

        //Making the head as the current address
            tempHead = tempNode;
            printf("Temp \n");
        printf("NODE temp : %p \n",tempNode);
        printf("NODE head: %p \n",tempHead);
        i++;

        }
     }else{
         printf("The file cannot be opened. :< \n");
         perror("Error at line 50");
     }
     turnLights(tempHead);
     return tempHead;
}
}

我得到以下结果：

NODE : 0x7fffe5462ac0
blue
Temp value : 0x7fffeda80d28
0x7fffeda80d1c
2
0
0x7fffeda80d20
Temp
NODE temp : 0x7fffe5462ac0
NODE head: 0x7fffe5462ac0
NODE : 0x7fffe5462b40
green
Temp value : 0x7fffeda80d28
0x7fffeda80d1c
1
0
0x7fffeda80d20
Temp
NODE temp : 0x7fffe5462b40
NODE head: 0x7fffe5462b40
NODE : 0x7fffe5462bc0
red
Temp value : 0x7fffeda80d28
0x7fffeda80d1c
1
0
0x7fffeda80d20
Temp
NODE temp : 0x7fffe5462bc0
NODE head: 0x7fffe5462bc0
NODE : 0x7fffe5462c40
yellow
Temp value : 0x7fffeda80d28
0x7fffeda80d1c
2
0
0x7fffeda80d20
Temp
NODE temp : 0x7fffe5462c40
NODE head: 0x7fffe5462c40
NODE : 0x7fffe5462cc0
blue
Temp value : 0x7fffeda80d28
0x7fffeda80d1c
1
0
0x7fffeda80d20
Temp
NODE temp : 0x7fffe5462cc0
NODE head: 0x7fffe5462cc0

变量 tempValue 在我的所有运行中具有相同的地址。这对于其他变量也是一样的。当我运行代码时，我只得到地址 0x7ffeda80d28 和 0x7ffffeda80d1c。如何修复此错误？

标签： c

解决方案

您正在获取分配在堆栈（指针）上的变量的地址。除非您从调用堆栈中的其他位置（例如调用函数或另一个函数）调用，否则这些变量在函数调用中将具有相同的地址。指针的地址和它们指向的地址不相同。

为了说明差异（以及堆栈地址如何工作）......

#include <stdlib.h>
#include <stdio.h>

void f1(int x) {

  int* p = &x;

  printf("address of pointer (stack): %p\n", &p);
  printf("pointer (stack): %p\n", p);

  // change pointer to a heap address

  p = malloc(sizeof(int));

  printf("pointer (heap): %p\n", p);
  printf("address of pointer (stack): %p\n", &p);

  free(p);
}

void f2(int x) {

  int y = x;

  f1(x);
}

int main(int argc, char *argv[]) {

  int x = 0;

  printf("f1:\n");
  f1(x);

  printf("\nf1 (again):\n");
  f1(x);

  printf("\nf2:\n");
  f2(x);

  return 0;
}

输出...

f1:
address of pointer (stack): 0x7ffcdcc52df0
pointer (stack): 0x7ffcdcc52dfc
pointer (heap): 0x9486b0
address of pointer (stack): 0x7ffcdcc52df0

f1 (again):
address of pointer (stack): 0x7ffcdcc52df0
pointer (stack): 0x7ffcdcc52dfc
pointer (heap): 0x9486b0
address of pointer (stack): 0x7ffcdcc52df0

f2:
address of pointer (stack): 0x7ffcdcc52dd0
pointer (stack): 0x7ffcdcc52ddc
pointer (heap): 0x9486b0
address of pointer (stack): 0x7ffcdcc52dd0

请注意，当您分配tempValue但为其分配值时，您也会泄漏内存strtok。

token = strtok(fileInfo,",");
char*  tempValue= malloc(50);
tempValue = token;

同样tempValue是一个指针，您正在将值从堆地址更改为由strtok. 所以返回的地址malloc丢失了，内存泄漏了（因为它不能用 来返回到堆中free）。通常，任何对 的调用都malloc应该有对 的相应调用free，否则您的程序正在泄漏内存。

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