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我正在尝试研究如何为分配创建动态数组，但无论我做什么，我的程序在输入 3 个或更多条目后都会继续挂起。

我没有收到任何错误，并且必须手动关闭控制台窗口，但是没有任何方向，我不确定我到底做错了什么。

如果我在控制台中创建 3 个以上的结构，无论我改变什么，我的程序在输入“n”以结束新事件的创建后都会挂起。

int readEvents(Event* ev_ptr[], int size)
{
    char answer = 'y', slash;
    int i = 0;

    cout << "\nCreate an event [y/n]? ";
    cin >> answer;
    cin.ignore();
    while (answer == 'y' || answer == 'Y')
    {
        ev_ptr[i] = new Event;

        cout << "\nEnter description: ";
        cin.getline(ev_ptr[i]->desc, 80, '\n');

        cout << "\nEnter date: ";
        cin >> ev_ptr[i]->date.month >> slash >> ev_ptr[i]->date.day >> slash >> ev_ptr[i]->date.year;
        cin.ignore();

        cout << "\nEnter time: ";
        cin >> ev_ptr[i]->time.hour >> slash >> ev_ptr[i]->time.minute;
        cin.ignore();

        i++;

        cout << "\nCreate an event [y/n]? ";
        cin >> answer;
        cin.ignore();
    }

    return i;
}

任何帮助，将不胜感激

编辑：

这是我声明 ev_ptr 数组大小的主要函数：

int main()
{
    Event* event_pointers[100];
    int count = readEvents(event_pointers, 100), userMonth;
    char userString[80];

    cout << "\nEnter a search string: ";
    cin.getline(userString, 80, '\n');
    cin.ignore();

    linsearch(event_pointers, count, userString);

    cout << "\nEnter a month to list Events for: ";
    cin >> userMonth;
    cin.ignore();

    binsearch(event_pointers, count, userMonth);

    for (int j = 0; j < count; j++) //Cleanup loop
        delete event_pointers[j];

    cout << "\nPress any key to continue...";
    (void)_getch();
    return 0;
}
4

2 回答 2

0

你为什么不使用std::vectorand std::unique？

#include <vector>
#include <memory>

class Event { }

int main()
{
  std::vector<std::unique_ptr<Event>> events;
  readEvents(events);
}

int readEvents(std::vector<std::unique_ptr<Event>>& events, int size)
{
  ...
  while (answer == 'y' || answer == 'Y')
  {
    ev_ptr[i] = std::make_unique<Event>();
    ...
  }
}
于 2019-11-29T07:38:16.027 回答
0

使用newanddelete在某种程度上是旧的做事方式。作为旧的做事方式，有数十年的代码使用它。正如我在上面的评论中总结的那样，您当前声明100 了 pointers-to-type Event，然后用于new为每个单独的struct Event实例分配存储空间。通过使用一个固定的指针数组——你被锁定在没有你最初声明指针的事件中。这是一种非常不灵活的方式。

相反，只需声明一块内存来保存一些初始事件数，并为分配的元素数和填充的元素数保留一对计数器。当 时filled == allocated，只需分配另一块内存（比如保存两倍于当前元素的元素），然后将数据从原始块复制到新块，删除原始块，并根据需要重复多次。（您基本上是在realloc()使用new/delete.

下面是一个简短的例子。在示例中，我使用了简化的Event结构。（您可以将日期和时间进一步拆分为yyyy-mm-dd和H:M:S）。该示例首先分配 2 个实例，Event然后继续读取与用户一样多的输入，更新分配大小并根据需要将原始复制到新的。初始设置和重新分配代码如下：

#include <iostream>
#include <cstring>

#define MAXDESC  80    /* max description length */
#define MAXDTTM  32    /* max date/time lengths */
#define EVSIZE    2    /* initial number of Event elements allocated */

struct Event {
    char desc[MAXDESC];
    char date[MAXDTTM];
    char time[MAXDTTM];
};

/** reallocate e to twice 'size' elements */
Event *reallocEVx2 (Event *e, size_t *size)
{
    Event *tmp = new Event[*size * 2];      /* allocate new block 2x in size */

    std::memcpy (tmp, e, *size * sizeof *e);    /* copy old to new */
    delete[] e;                                 /* delete old */
    *size *= 2;                                 /* update allocated size */

    return tmp;     /* return pointer to new block */
}

该readEvents()函数将原始指针的地址作为参数，因为开始地址会在重新分配时发生变化。因此，您可以从调用者那里传递指针的地址，而不是仅仅传递一个指针，这样您就可以更新该地址以指向新重新分配的内存块readEvents()。由于您正在对原始指针地址进行操作，因此将在调用者中看到该更改。如果您没有传递原始指针的地址，则必须返回一个指向新分配块的指针，并将其分配给调用者中的指针。

for 的实现readEvents()取消了混合getline和>>on std::cin。取而代之的是简单地使用getline并从每一行创建一个stringstream，以进一步将数据分离为使用字符串流>>上的单个值。这消除了无效输入无法读取并在输入流中保持未读状态的可能性，只是在等待下一个输入。

稍微重写您的readEvents()简单循环，直到用户输入提示时以外的其他内容'y'：

/** read events from user reallocating as required
 *  (note: must pass address-of-pointer, not just pointer)
 */
size_t readEvents (Event **e, size_t *nelem, size_t *size)
{
    char buf[MAXDESC];

    for (;;) {  /* loop continually until something other than 'y' entered */
        std::cout << "\nCreate event (y/n)? ";
        if (!std::cin.getline (buf, sizeof buf) || *buf != 'y')
            break;

        if (*nelem == *size)    /* check if realloc needed */
            *e = reallocEVx2 (*e, size);

        /* get input */
        std::cout << "  Enter description: ";
        if (!std::cin.getline ((*e)[*nelem].desc, MAXDESC))
            break;

        std::cout << "  Enter date: ";
        if (!std::cin.getline ((*e)[*nelem].date, MAXDTTM))
            break;
        /* create stringstream to parse date into yyyy-mm-dd here */

        std::cout << "  Enter time: ";
        if (!std::cin.getline ((*e)[*nelem].time, MAXDTTM))
            break;
        /* create stringstream to parse time into H:M:S here */

        (*nelem)++;     /* update no. of elements filled */
    }
    return *nelem;      /* return no. of elements filled */
}

在main()中，您只需声明您的计数器来跟踪分配的元素数量（size如下）和使用的元素数量（nelem如下），并为最初的两个实例分配Event并开始读取数据。代码通过输出内存统计信息（分配的元素/使用的元素）完成并输出每个存储Event的实例，例如

int main (void) {

    size_t nelem = 0;
    size_t size = EVSIZE;
    Event *events = new Event[size];    /* allocate initial 'size' elements */

    if (!readEvents (&events, &nelem, &size)) {     /* read/fill events */
        std::cerr << "error: no events read.\n";
        return 1;
    }

    /* output memory useage (elements allocated/filled) */
    std::cout << "\nelements allocated: " << size <<
                 "\nelements filled   : " << nelem << "\n\n"; 

    for (size_t i = 0; i < nelem; i++)  /* output all events */
        std::cout << events[i].desc << "    " << events[i].date << "    " <<
                    events[i].time << '\n';

    delete[] events;    /* free memory  */
}

总而言之，你可以这样做：

#include <iostream>
#include <cstring>

#define MAXDESC  80    /* max description length */
#define MAXDTTM  32    /* max date/time lengths */
#define EVSIZE    2    /* initial number of Event elements allocated */

struct Event {
    char desc[MAXDESC];
    char date[MAXDTTM];
    char time[MAXDTTM];
};

/** reallocate e to twice 'size' elements */
Event *reallocEVx2 (Event *e, size_t *size)
{
    Event *tmp = new Event[*size * 2];      /* allocate new block 2x in size */

    std::memcpy (tmp, e, *size * sizeof *e);    /* copy old to new */
    delete[] e;                                 /* delete old */
    *size *= 2;                                 /* update allocated size */

    return tmp;     /* return pointer to new block */
}

/** read events from user reallocating as required
 *  (note: must pass address-of-pointer, not just pointer)
 */
size_t readEvents (Event **e, size_t *nelem, size_t *size)
{
    char buf[MAXDESC];

    for (;;) {  /* loop continually until something other than 'y' entered */
        std::cout << "\nCreate event (y/n)? ";
        if (!std::cin.getline (buf, sizeof buf) || *buf != 'y')
            break;

        if (*nelem == *size)    /* check if realloc needed */
            *e = reallocEVx2 (*e, size);

        /* get input */
        std::cout << "  Enter description: ";
        if (!std::cin.getline ((*e)[*nelem].desc, MAXDESC))
            break;

        std::cout << "  Enter date: ";
        if (!std::cin.getline ((*e)[*nelem].date, MAXDTTM))
            break;
        /* create stringstream to parse date into yyyy-mm-dd here */

        std::cout << "  Enter time: ";
        if (!std::cin.getline ((*e)[*nelem].time, MAXDTTM))
            break;
        /* create stringstream to parse time into H:M:S here */

        (*nelem)++;     /* update no. of elements filled */
    }

    return *nelem;      /* return no. of elements filled */
}

int main (void) {

    size_t nelem = 0;
    size_t size = EVSIZE;
    Event *events = new Event[size];    /* allocate initial 'size' elements */

    if (!readEvents (&events, &nelem, &size)) {     /* read/fill events */
        std::cerr << "error: no events read.\n";
        return 1;
    }

    /* output memory useage (elements allocated/filled) */
    std::cout << "\nelements allocated: " << size <<
                 "\nelements filled   : " << nelem << "\n\n"; 

    for (size_t i = 0; i < nelem; i++)  /* output all events */
        std::cout << events[i].desc << "    " << events[i].date << "    " <<
                    events[i].time << '\n';

    delete[] events;    /* free memory  */
}

示例使用/输出

$ ./bin/events_new-del

Create event (y/n)? y
  Enter description: Event 1
  Enter date: 11/29/19
  Enter time: 12:30:31

Create event (y/n)? y
  Enter description: Event 2
  Enter date: 11/29/19
  Enter time: 12:30:41

Create event (y/n)? y
  Enter description: Event 3
  Enter date: 11/29/19
  Enter time: 12:30:51

Create event (y/n)? y
  Enter description: Event 4
  Enter date: 11/29/19
  Enter time: 12:31:01

Create event (y/n)? y
  Enter description: Event 5
  Enter date: 11/29/19
  Enter time: 12:31:11

Create event (y/n)? n

elements allocated: 8
elements filled   : 5

Event 1    11/29/19    12:30:31
Event 2    11/29/19    12:30:41
Event 3    11/29/19    12:30:51
Event 4    11/29/19    12:31:01
Event 5    11/29/19    12:31:11

如果您对这种方法还有其他问题，请仔细查看并告诉我。

于 2019-11-29T19:32:37.687 回答