c - 如何在 C 中为我的数据结构分配内存

Question

我不明白为什么我的代码在用户输入他们的数据后打印出垃圾变量。在我的intro to C class中学习数据结构，链表和内存分配的过程中。感谢您的帮助!

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

typedef struct AutoMobilesInfo
{
    char *Manufacturer, *ModelNameOfCar, *ColorOfCar;
    int YearOfCar;
    struct AutoMobilesInfo *next;
} Car;

void EnterCarInfo(Car *Info)
{
    Info = (Car *)malloc(sizeof(Car));
    Info->Manufacturer = (char *)malloc(12 *(sizeof(char)));
    Info->ModelNameOfCar = (char *)malloc(12 *(sizeof(char)));
    Info->ColorOfCar = (char *)malloc(12 *(sizeof(char)));

    printf("Please enter the car's manufacturer: \n");
    scanf(" %s", Info->Manufacturer);
    printf("Please enter the car's model: \n");
    scanf(" %s", Info->ModelNameOfCar);
    printf("Please enter the car's color: \n");
    scanf(" %s", Info->ColorOfCar);
    printf("Please enter the year the car was made: \n");
    scanf("%d", &Info->YearOfCar);
}

void PrintedOutCarInfo(Car *host)
{
    host = (Car *)malloc(sizeof(Car));
    host->Manufacturer = (char *)malloc(12 *(sizeof(char)));
    host->ModelNameOfCar = (char *)malloc(12 *(sizeof(char)));
    host->ColorOfCar = (char *)malloc(12 *(sizeof(char)));

    printf("The car's manufacturer is %s\n", host->Manufacturer);
    printf("The car's model is %s\n", host->ModelNameOfCar);
    printf("The color of the car is %s\n", host->ColorOfCar);
    printf("The year the car was made is %d\n", host->YearOfCar);
}

int main()
{
    Car *Car1;
    Car1 = (Car *) malloc(sizeof(Car));
    EnterCarInfo(Car1);
    PrintedOutCarInfo(Car1);
    free(Car1);

    return 0;
}

Answer 1

您正在覆盖 PrintedOutCarInfo 中的指针。这条线

host = (Car *)malloc(sizeof(Car));

还有这一行

Info = (Car *)malloc(sizeof(Car));

你传入的变量host和Info被分配了。把那个函数改成这个

void PrintedOutCarInfo(Car *host) {
  printf("The car's manufacturer is %s\n", host->Manufacturer);
  printf("The car's model is %s\n", host->ModelNameOfCar);
  printf("The color of the car is %s\n", host->ColorOfCar);
  printf("The year the car was made is %d\n", host->YearOfCar);
}

您也不应该对 malloc 的返回进行 case，即改为这样做...

 Info = malloc(sizeof(Car));

试试这个...

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

typedef struct AutoMobilesInfo
{
  char *Manufacturer, *ModelNameOfCar, *ColorOfCar;
  int YearOfCar;
  struct AutoMobilesInfo *next;
} Car;

void EnterCarInfo(Car *Info)
{
  Info->Manufacturer   = malloc(12 * (sizeof(char)));
  Info->ModelNameOfCar = malloc(12 * (sizeof(char)));
  Info->ColorOfCar     = malloc(12 * (sizeof(char)));

  printf("Please enter the car's manufacturer: \n");
  scanf(" %s", Info->Manufacturer);
  printf("Please enter the car's model: \n");
  scanf(" %s", Info->ModelNameOfCar);
  printf("Please enter the car's color: \n");
  scanf(" %s", Info->ColorOfCar);
  printf("Please enter the year the car was made: \n");
  scanf("%d", &Info->YearOfCar);
}

void PrintedOutCarInfo(Car *host) {
  printf("The car's manufacturer is %s\n", host->Manufacturer);
  printf("The car's model is %s\n", host->ModelNameOfCar);
  printf("The color of the car is %s\n", host->ColorOfCar);
  printf("The year the car was made is %d\n", host->YearOfCar);
}

int main()
{
  Car *Car1 = malloc(sizeof(Car));
  EnterCarInfo(Car1);
  PrintedOutCarInfo(Car1);
  free(Car1);
  return 0;
}