如何操作过载“"? [英] How to operate overload ">>"?

问题描述

Product **products;

int numProducts = 0;

void setup()
{
    ifstream finput("products.txt");
    //get # of products first.
    finput >> numProducts;
    products = new Product* [numProducts];

    //get product codes, names & prices.
    for(int i=0; i<numProducts; i++) {
        products[i] = new Product;
        finput >> products[i]->getCode() >> products[i]->getName() >> products[i]->getPrice();
    }
}

此行出现对二进制表达式无效的操作数"错误:

I am getting an "invalid operands to binary expression" error for this line:

finput >> products[i]->getCode() >> products[i]->getName() >> products[i]->getPrice();

我是否需要操作符重载>>，我该怎么办?

Do I need to operator overload >> and how would I do it?

推荐答案

让我们举一个非常简单的示例，假设Product的基本定义为:

Let's take a very simple example, assuming a basic definition for Product as:

class Product
{
   int code;
   string name;
   double price;

public:
   Product(int code, const std::string& name, double price)
      : code{code}, name{name}, price{price}
   {}

   int getCode() const { return code; }
   const std::string& getName() const { return name; }
   double getPrice() const { return price; }
};

您不能直接使用operator>>来读入到getCode()，getName()或getPrice()的返回值中.这些用于访问这些值.

You can't read in using operator>> directly into the return values from getCode(), getName() or getPrice(). Those are for accessing those values.

相反，您需要读入值并从这些值构造产品，如下所示:

Instead, you need to read in the values and construct products from those values like this:

for(int x = 0; x < numProducts; ++x)
{
   int code = 0;
   string name;
   double price = 0;

   finput >> code >> name >> price;
   products[i] = new Product{code,name,price};
}

现在，您可以将其重构为operator>>:

Now, you could refactor this into operator>>:

std::istream& operator>>(std::istream& in, Product& p)
{
   int code = 0;
   string name;
   double price = 0;

   in >> code >> name >> price;
   p = Product{code,name,price};
   return in;
}

关于此代码，还有很多其他事情要考虑:

There are a bunch of other things to consider about this code:

• 使用std::vector<Product>而不是您自己的数组
• 如果name有空格，以下示例将不起作用
• 没有错误检查，operator>> 可以失败

• Use std::vector<Product> instead of your own array
• The examples below won't work if name has spaces
• There's no error checking and operator>> can fail

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