Question

我之前尝试过使用for循环来放入数据，但问题太多了。所以我尝试使用while循环，但是当我尝试调试它时，它继续将-858993460放入每个插槽。 .dat文件位于正确位置并打开。

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

struct record
{
    int item_id;
    string item_type;
    float item_price;
    int num_stock;
    string item_title;
    string item_author;
    int year_published;
};

void read_all_records(record records[], int &valid_entries);
int num_inventory_of_type(record records[], string type, int &valid_entries);
const int max_array = 100;
int main()
{
    int valid_entries = 0;
    record records[max_array];
    read_all_records(records, valid_entries);

    cout << "Stock Report" << endl;
    cout << "------------" << endl;
    int book = num_inventory_of_type(records, "book", valid_entries);
    cout << "Book's In Stock: " << book << endl;
    int cd = num_inventory_of_type(records, "cd", valid_entries);
    cout << "CD's In Stock: " << cd << endl;
    int dvd = num_inventory_of_type(records, "dvd", valid_entries);
    cout << "DVD's In Stock: " << dvd << endl;

    return 0;
}

void read_all_records(record records[], int &valid_entries)
{
    ifstream invfile;
    invfile.open("inventory.dat"); 
    if (!invfile.is_open())
    {
        cout<<"file open failed";
        exit(1);
    }
    while(invfile.good() && valid_entries < max_array)
    {
        invfile >> records[valid_entries].item_id >> records[valid_entries].item_type
            >> records[valid_entries].item_price >> records[valid_entries].num_stock
            >> records[valid_entries].item_title >> records[valid_entries].item_author
            >> records[valid_entries].year_published;
        if(!invfile.good())
            break;
        valid_entries++;

    }
    invfile.close();

}
int num_inventory_of_type(record records[], string type, int &valid_entries)
{
    int count = 0;
    int holder = 0;
    for (int count = 0; count<valid_entries; count++);
    {       
        if (records[count].item_type == type)
        {
            holder+=records[count].num_stock;

        }
    }

    return holder;
}

.dat文件是

123456
book
69.99
16
Problem_Solving_With_C++
Walter_Savitch
2011
123457
cd
9.99
32
Sigh_No_More
Mumford_and_Sons
2010
123458
dvd
17.99
15
Red_State
Kevin_Smith
2011
123459
cd
9.99
16
The_Church_Of_Rock_And_Roll
Foxy_Shazam
2012
123460
dvd
59.99
10
The_Walking_Dead_Season_1
Robert_Kirkman
2011

所有人都在新线上，没有空格。

基本上它应该启动，运行read_all_records函数并将.dat数据放入数组中。但是，我将cout << records[count].item_id;放在while循环中只是为了查看数据是否实际进入，每次都得到-858993460。之后，它应该运行下一个功能3次并返回每本书的数量。

Answer 1

这不是问题的直接答案，但也许它会在重构后消失：

std::istream& operator>>(std::istream& is, record& r) {
    return is >> r.item_id >> r.item_type >> … >> r.year_published;
}

int main () {
    if (std::ifstream invfile("inventory.dat")) {
        std::vector<record> records((std::istream_iterator<record>(invfile)),
                                     std::istream_iterator<record>());

        num_inventory_of_type(records, "dvd");
        num_inventory_of_type(records, "cd");
        num_inventory_of_type(records, "book");
    }
}

如果您仍想在阅读时打印出每条记录，可以按如下方式重新排列代码：

        std::vector<record> records;
        for (std::istream_iterator<record> i(invfile);
             i != std::istream_iterator<record>(); ++i)
        {
            records.push_back(*i);
            std::cout << i->item_id << "\n";
        }

Answer 2

您在int上使用了整数类型item_price。然后，invfile >> records[count].item_price只会提取69而不是69.99，因此当您尝试提取year_published时会导致错误。

改为使用float或double。

struct record
{
    int item_id;
    string item_type;
    float item_price;
    int num_stock;
    string item_title;
    string item_author;
    int year_published;
};

/* skipped identical lines */

while(invfile.good() && count < max_array)
{
    invfile >> records[count].item_id >> records[count].item_type
        >> records[count].item_price >> records[count].num_stock
        >> records[count].item_title >> records[count].item_author
        >> records[count].year_published;
        cout << records[count].item_price << endl;
        if(!invfile.good())
            break;
    cout << records[count].item_id << endl;
        count++;
}
invfile.close();

请注意，for (int count = 0; count<max_array; count++);中有一个额外的分号。我想你不打算这样做，所以删除它。

Answer 3

您需要更改int item_price;到浮动所以 - ＆gt; float item_price;

并且如上所述，您需要交换计数++;和cout＆lt;＆lt;记录[count] .item_id line。

完成这两项更改后，它将正常运行。

struct record
{
    int item_id;
    string item_type;
    float item_price; // <--- Needs to be a float
    int num_stock;
    string item_title;
    string item_author;
    int year_published;
};


// This order is required because you are storing in the current 'count' record and then you need to print it.  Then increment the count to store the next record  
cout << records[count].item_id;
count++;

WHILE循环和数据输入

3 个答案: