結構數組中的動態分配內存（在C中）

Question

我無法弄清楚如何動態地將內存分配給數組結構。我需要使用我定義的結構數組，以便可以遍歷它來打印信息。但是，我也被要求動態地分配內存給數組。

問題是，當我在代碼中使用malloc（）（您將看到它被註釋掉）時，它會將指針從數組索引中拋出。有什麼辦法來完成動態分配內存，同時指向數組指示存儲數據？

免責聲明：我對C非常陌生，如果我的編碼傷害了你的眼睛，我提前誠摯道歉。只是想了解該計劃，而不是快速完成它。

程序指令：

編寫使用 '結構' 定義包含以下學生的結構的C程序：

信息：

1. 初始[字符]
2. 年齡[整數]
3. Id [整數]
4. 等級[character]

你的程序應該爲5名學生打印上述信息。

提示：使用結構數組並遍歷數組以打印信息。

創建具有結構：int類型

稱爲標籤A字符指針的

1. 可變數據。這個指針應該指向一個字符串的地址。

檢查內存是否可用，然後動態分配所需內存到您的結構。

將值分配給您的結構變量並將其打印到控制檯。

到目前爲止的代碼：

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

int main (void) 
{ 
    struct student 
    { 
     char initial [21]; 
     int age; 
     float id; 
     char grade [3]; 
    } list[5]; 

    struct student * tag = list; 

    //LINE BELOW IS WHAT I WAS TRYING TO DO; BUT THROWS POINTER OFF OF STRUCT ARRAY 
    //tag = (struct student *) malloc (sizeof (struct student)); 
    strcpy(tag->initial, "KJ"); 
    tag->age = 21; 
    tag->id = 1.0; 
    strcpy (tag->grade, "A"); 
    tag++; 

    strcpy(tag->initial, "MJ"); 
    tag->age = 55; 
    tag->id = 1.1; 
    strcpy (tag->grade, "B"); 
    tag++; 

    strcpy(tag->initial, "CJ"); 
    tag->age = 67; 
    tag->id = 1.2; 
    strcpy (tag->grade, "C"); 
    tag++; 

    strcpy(tag->initial, "SJ"); 
    tag->age = 24; 
    tag->id = 1.3; 
    strcpy (tag->grade, "D"); 
    tag++; 

    strcpy(tag->initial, "DJ"); 
    tag->age = 27; 
    tag->id = 1.4; 
    strcpy (tag->grade, "F"); 
    tag++; 

    int n; 

    for (n = 0; n < 5; n++) { 
      printf ("%s is %d, id is %f, grade is %s\n", 
       list [ n ].initial, list [ n ].age, list [ n ].id, list [ n ].grade); 
      } 

    return 0; 

} 

Answer 1

試試這個....我在這裏聲明一個結構指針tag。我爲5個學生結構分配記憶。分配值後，現在tag指向最後一個值，所以我減少了5次。這個程序只使用一個指針。如果你想要，你可以嘗試使用數組指針。

我在節目中提到的變化，爲//changes

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

int main (void) 
{ 
struct student 
    { 
    char initial [21]; 
    int age; 
    float id; 
    char grade [3]; 
    } list[5]; 

struct student * tag; 


    tag = (struct student *) malloc (5* sizeof (struct student));//changes 

strcpy(tag->initial, "KJ"); 
tag->age = 21; 
tag->id = 1.0; 
strcpy (tag->grade, "A"); 
tag++; 

strcpy(tag->initial, "MJ"); 
tag->age = 55; 
tag->id = 1.1; 
strcpy (tag->grade, "B"); 
tag++; 

strcpy(tag->initial, "CJ"); 
tag->age = 67; 
tag->id = 1.2; 
strcpy (tag->grade, "C"); 
tag++; 

strcpy(tag->initial, "SJ"); 
tag->age = 24; 
tag->id = 1.3; 
strcpy (tag->grade, "D"); 
tag++; 

strcpy(tag->initial, "DJ"); 
tag->age = 27; 
tag->id = 1.4; 
strcpy (tag->grade, "F"); 
tag++; 

int n; 
    tag=tag-5;//changes 

for (n = 0; n < 5; n++) { 
     printf ("%s is %d, id is %f, grade is %s\n", 
      tag->initial, tag->age, tag->id, tag->grade); 
      tag++;//changes 
     } 

return 0; 
} 

使用品特的陣列......（而不是使用單獨的任務，你可以使用循環分配值，以每一個學生）

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

    int main (void) 
    { 
      struct student 
      { 
      char initial [21]; 
      int age; 
      float id; 
      char grade [3]; 
      } list[5]; 

     struct student *tag[5]; 
    int i; 

    for(i=0;i<5;i++) 
    tag[i]= (struct student *) malloc (sizeof (struct student)); 

     strcpy(tag[0]->initial, "KJ"); 
     tag[0]->age = 21; 
     tag[0]->id = 1.0; 
     strcpy (tag[0]->grade, "A"); 

     strcpy(tag[1]->initial, "MJ"); 
     tag[1]->age = 55; 
     tag[1]->id = 1.1; 
     strcpy (tag[1]->grade, "B"); 

     strcpy(tag[2]->initial, "CJ"); 
     tag[2]->age = 67; 
     tag[2]->id = 1.2; 
     strcpy (tag[2]->grade, "C"); 

     strcpy(tag[3]->initial, "SJ"); 
     tag[3]->age = 24; 
     tag[3]->id = 1.3; 
     strcpy (tag[3]->grade, "D"); 

     strcpy(tag[4]->initial, "DJ"); 
     tag[4]->age = 27; 
     tag[4]->id = 1.4; 
     strcpy (tag[4]->grade, "F"); 

     for (i = 0; i < 5; i++) 
     { 
       printf ("%s is %d, id is %f, grade is %s\n", 
      tag[i]->initial, tag[i]->age, tag[i]->id, tag[i]->grade); 

     } 

     return 0; 

    } 

Answer 2

如果您使用指針讀取並打印結構值，則不需要數組。如果你正在嘗試使用數組，那麼這是做到這一點的方法。

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

    int main (void) 
    { 
     struct student 
     { 
      char initial [21]; 
      int age; 
      float id; 
      char grade [3]; 
     } list[5]; 

     struct student *tag = (struct student *) malloc (sizeof (struct student) * 5); 

     int i; 
     for(i=0;i<5;i++) 
     { 
      printf("Enter the student initial\n"); 
      scanf("%s",list[i].initial); 
      printf("Enter the student age\n"); 
      scanf("%d",&list[i].age); 
      printf("Enter the student id\n"); 
      scanf("%f",&list[i].id); 
      printf("Enter the grade\n"); 
      scanf("%s",list[i].grade); 
      tag++; 
     } 

     int n; 

     for (n = 0; n < 5; n++) { 
      printf ("%s is %d, id is %f, grade is %s \n", 
       list [ n ].initial, list [ n ].age, list [ n ].id, list [ n ].grade); 
     } 

     return 0; 

    }