使用 malloc 创建指向多个结构项的指针

Question

对于一个 c 编程类，我被告知使用 typedefs 按顺序创建以下结构：

//STRUCTS
struct time {
    unsigned int hour;
    unsigned int minute;
    unsigned int second;
};//end struct time
struct date {
    unsigned int month;
    unsigned int day;
    unsigned int year;
};//end struct Date
struct event {
    char name[20];
    struct time* time;
    struct date* date;
};//end struct event

//TYPEDEFS
typedef struct time Time;
typedef struct date Date;
typedef struct event Event;

我应该从那里询问要创建的最大事件数，然后为那么多事件分配一个具有足够内存的指针。我的部分工作是：

Event *events;

//Ask for max number of events and allocate memory
printf("Number of events to add: ");
scanf("%d", &numEvents);
events = (Event*) malloc(sizeof(Event) * numEvents);

但是，从那里我不确定如何遍历指针以查看特定事件。我知道它不仅仅是一个数组，所以 events[i] 不起作用。但除此之外，我迷路了。我获取事件的（损坏的）功能是：

void getEvent(Event *events, int index){
    //variables
    char title[20];
    unsigned int day, month, year, hour, minute, second;
    Event tempEvent;


    //Ask for input
    printf("Input title, date, and time.\n");
    if(index == 0)
        printf("example -> title: dd/mm/yy hh:mm:ss\n");

    //Take input
    scanf("%20[^:]: %u/%u/%u %u:%u:%u", title, &day, &month, &year, &hour, &minute, &second);


    tempEvent = (Event) {*title, { hour, minute, second }, { month, day, year } };

    events[index] = tempEvent;      
}

我知道这是不对的，我在测试时遇到了分段错误。

当我编译时，我收到这些警告（以及一些关于类似事情的重复）：

Lab4.c: In function ‘getEvent’: Lab4.c:82:2: warning: braces around scalar initializer 
tempEvent = (Event) {*title, { hour, minute, second }, { month, day, year } }; 
^ Lab4.c:82:2: note: (near initialization for ‘(anonymous).name[1]’)

Lab4.c:82:39: warning: excess elements in scalar initializer 
tempEvent = (Event) {*title, { hour, minute, second }, { month, day, year } }

Answer 1

编译器告诉你第 82 行是一团糟。

tempEvent = (Event) {*title, { hour, minute, second }, { month, day, year } };

特别是event 结构的第一个成员是数组char name[20]，但您尝试使用单个字符*title 对其进行初始化。但更大的问题是time 和date（在event 结构中）是指针，而您没有为这些指针分配任何内存。

一种解决方案是分配内存，然后让scanf 填写值，如下所示：

void getEvent( Event *events, int n )
{
    // allocate memory
    events[n].time = malloc(sizeof(Time));
    events[n].date = malloc(sizeof(Date));
    if ( events[n].time == NULL || events[n].date == NULL )
    {   /* TODO: handle the error */ }

    //Ask for input
    printf("Input title, date, and time.\n");
    if ( n == 0 )
        printf("example -> title: dd/mm/yy hh:mm:ss\n");

    //Take input
    int count = scanf( "%20[^:]:%u/%u/%u%u:%u:%u", events[n].name,
                       &events[n].date->day, &events[n].date->month, &events[n].date->year,
                       &events[n].time->hour, &events[n].time->minute, &events[n].time->second );
    if ( count != 7 )
    {   /* TODO: handle the error */ }
}