Scanf into struct包含指向不同结构的指针 [英] Scanf into struct containing pointer to different struct

问题描述

这个函数将书籍信息插入到结构中..它运作良好但是当扫描日期程序崩溃时...我搜索了很多但无法修复它

 typedef struct 
 {
 char title [10]; 
 char author [10]; 
 char publisher [10]; 
 char ISBN [10]; 
 dateStruct * date; 
 int份; 
 int current; 
}预订; 
 typedef struct 
 {
 int day; 
 int month; 
 int year; 
} dateStruct; 
 
 book * insert（void）
 {
 book * theInserted =（book *）malloc（1 * sizeof（book））; 
得到（theInserted->标题）; 
得到（theInserted->作者）; 
得到（theInserted->发布商）; 
得到（theInserted-> ISBN）; 
 scanf（％d％d，&（theInserted-> copies），&（theInserted-> current））; 
 scanf（％d％d％d，&（theInserted-> date-> day），&（theInserted-> date-> month），&（theInserted->日期 - >年））; 
返回插入; 
} 

我的尝试：



这是出错的地方：

 scanf（％d％d％d，&（theInserted - > date-> day），&（theInserted-> date-> month），&（theInserted-> date-> year））; 

解决方案

您必须为 theInserted-> date 分配内存，并在不再使用时释放它：

 book * theInserted =（book *）malloc（sizeof（book））; 
 theInserted-> date =（dateStruct *）malloc（sizeof（dateStruct））; 
 
 / *使用此处插入* / 
 
 / *可用内存* / 
免费（theInserted-> date）; 
 free（theInserted）; 

如果不这样做， theInserted-> date 成员将指向导致访问冲突的任何地方或只是一个程序崩溃。



更好的解决方案是使 dateStruct 成员成为普通类型的成员，而不是指针：

 typedef struct 
 {
 char title [10]; 
 char author [10]; 
 char publisher [10]; 
 char ISBN [10]; 
 dateStruct日期; //普通成员而不是指针
 int copies; 
 int current; 
}预订; 
 
 / * ... * / 
 
 scanf（％d％d％d，&（theInserted-> date.day），&（theInserted - > date.month），及（theInserted-> date.year））; 

this function inserts a book info into structure .. it works well but when scanning the date the program crushes..I searched a lot but couldn't fix it

typedef struct
{
    char title[10];
    char author[10];
    char publisher[10];
    char ISBN[10];
    dateStruct* date;
    int copies;
    int current;
} book;
typedef struct
{
    int day;
    int month;
    int year;
} dateStruct;

book* insert(void)
{
   book* theInserted =(book*)malloc(1*sizeof(book));
   gets(theInserted->title);
   gets(theInserted->author);
   gets(theInserted->publisher);
   gets(theInserted->ISBN);
   scanf("%d%d",&(theInserted->copies),&(theInserted->current));
   scanf("%d%d%d",&(theInserted->date->day),&(theInserted->date->month),&(theInserted->date->year));
    return theInserted;
}

What I have tried:

this is where something goes wrong:

scanf("%d%d%d",&(theInserted->date->day),&(theInserted->date->month),&(theInserted->date->year));

解决方案

You must allocate memory for the theInserted->date and free it when no longer used:

book* theInserted =(book*)malloc(sizeof(book));
theInserted->date = (dateStruct*)malloc(sizeof(dateStruct));

/* Use theInserted here */

/* Free memory */
free(theInserted->date);
free(theInserted);

When not doing so, the theInserted->date member points to anywhere resulting in an access violation or just a program crash.

A better solution is to make the dateStruct member a normal type member and not a pointer:

typedef struct
{
    char title[10];
    char author[10];
    char publisher[10];
    char ISBN[10];
    dateStruct date; // normal member and not pointer
    int copies;
    int current;
} book;

/* ... */

scanf("%d%d%d",&(theInserted->date.day),&(theInserted->date.month),&(theInserted->date.year));

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