为什么getline函数在带有结构数组的for循环中不能多次工作? [英] Why won't getline function work multiple times in a for loop with an array of structures?

问题描述

我有一个小问题.我创建了一个程序，要求用户输入四个不同零件的零件名称和零件价格.每个名称和价格都填充一个结构，我有四个结构的数组.当我执行for循环以填充所有名称和价格时，我的getline功能无法正常工作，在输入第一部分的名称后，它只是跳过输入的部分.你能告诉我为什么吗? 这是我的代码:

I have a little problem. I've created a program that asks user to enter part's name and part's price for four diffrent parts. Each name and price fills a structure, and I have an array of four structures. When i do a for loop to fill all the names and prices, my getline functon doesn't work properly, it simply just skipps the entering part after I enter the first part's name. Can you please tell me why? Here's my code:

#include <iostream>
#include <string>

struct part {
    std::string name;
    double cost;
};

int main() {

    const int size = 4;

    part apart[size];

    for (int i = 0; i < size; i++) {
        std::cout << "Enter the name of part № " << i + 1 << ": ";
        getline(std::cin,apart[i].name);
        std::cout << "Enter the price of '" << apart[i].name << "': ";
        std::cin >> apart[i].cost;
    }
}

推荐答案

std::getline使用换行符\n，而std::cin将使用您输入并停止的数字.

std::getline consumes the newline character \n, whereas std::cin will consume the number you enter and stop.

要说明为什么会出现此问题，请为前两个部分"考虑以下输入:

To illustrate why this is a problem, consider the following input for the first two 'parts':

item 1\n
53.25\n
item 2\n
64.23\n

首先，您调用std::getline，它使用文本:item 1\n.然后调用std::cin >> ...，它识别53.25，对其进行解析，使用它并停止.然后，您将拥有:

First, you call std::getline, which consumes the text: item 1\n. Then you call std::cin >> ..., which recognises the 53.25, parses it, consumes it, and stops. You then have:

\n
item 2\n
64.23\n

然后您再次拨打std::getline.它所看到的只是一个\n，它被认为是一行的结尾.因此，它看到一个空字符串，什么都没有存储在std::string中，消耗了\n，然后停止.

You then call std::getline for a second time. All it sees is a \n, which is recognised as the end of a line. Therefore, it sees a blank string, stores nothing in your std::string, consumes the \n, and stops.

要解决此问题，您需要确保在使用std::cin >>存储浮点值时使用换行符.

To solve this, you need to make sure the newline is consumed when you store the floating-point value using std::cin >>.

尝试一下:

#include <iostream>
#include <string>
// required for std::numeric_limits
#include <limits>

struct part {
    std::string name;
    double cost;
};

int main() {

    const int size = 4;

    part apart[size];

    for (int i = 0; i < size; i++) {
        std::cout << "Enter the name of part № " << i + 1 << ": ";
        getline(std::cin,apart[i].name);
        std::cout << "Enter the price of '" << apart[i].name << "': ";
        std::cin >> apart[i].cost;

        // flushes all newline characters
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }
}

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