如何从字符串中提取浮点数？

Question

我需要读取一行包含字母、整数和浮点数的文本，然后计算这些浮点数。到目前为止我所做的低于

           while (getline(readSearch, line))
    {
        while (line.find(letters[0])!=string::npos ||   line.find(letters[1])!=string::npos || line.find(letters[2])!=string::npos || line.find(letters[3])!=string::npos || line.find(letters[4])!=string::npos)
        {
            cout << line << "\n";
            break;
        }

这是我正在读取的文件

   Chips 01c [=11=].50
   Juice  02j  .5
   Chocolate 03c .00
   Pen 04p 0.20
   Backpack 05b .00
   Bag 06b .25
   Ball 07b .50
   Toy 08t .22
   Wi-Fi Router 09wr .00
   Generic HDMI cable 010hc .00

由于此文件包含三种不同类型的数据，我真的很难弄清楚如何只计算那些代表价格的浮点数。我需要以某种方式将它们输入到变量中而不是执行计算。

Answer 1

find the appropriate delimiter to locate the substr you're interested in, then use a stringstream 转换为 float/double。 wstring 操作有等效的 std 对象。

Answer 2

Since this file contains three different types

你应该定义三种不同的类型。为每种类型定义输入运算符。然后为这行数据定义一个类型，你就可以读入三种不同的类型。

数据线

struct DataLine
{
    std::string name;   // Wi-Fi Router
    DataBlob    blob;   // 010hc 
    Price       price;  // .00

    void swap(DataLine& other) noexcept
    {
        using std::swap;
        swap(name,   other.name);
        swap(blob,   other.blob);
        swap(price,  other.price);
    }

    friend std::istream& operator>>(std::istream& s, DataLine& data)
    {
        std::string line;
        if (std::getline(s, line))
        {
            // The name takes up all but the last two space separated words.
            // So find that point first.
            std::size_t  first  = line.find_last_of(" \t");
            std::size_t  second = (first == 0)
                                      ? std::string::npos 
                                      : line.find_last_of(" \t", first-1);
            std::stringstream lineStream(line);
            DataLine  tmp;
            if (lineStream >> ItemNameReader(tmp.name, second - 1) >> tmp.blob >> tmp.price) {
               // All three items were read correctly
               // So update the object with the new state.
               data.swap(tmp);
            }
            else {
               // One of the read operations failed.
               // So set the state of the stream to bad
               // The user can then handle this situation.
               s. setstate(std::ios::badbit);
            }
        }
        return s;
    }
};

ItemNameReader

struct ItemNameReader
{
    std::string&  name;
    std::size_t   size;
    ItemNameReader(std::string& name, std::size_t size)
        : name(name)
        , size(size)
    {}
    friend std::istream& operator>>(std::istream& s, ItemNameReader const& data)
    {
        data.name.resize(data.size);
        s.read(data.name.data(), data.size);
        return s;
    }   
};

DataBlob

class DataBlob
{
    std::string   blob;
    friend std::istream& operator>>(std::istream& s, DataBlob& data)
    {
        return s >> data.blob;
    }
};

价格

class Price
{
    char  units;
    float value;  // Though you may want to consider monetary
                  // units as integer values to avoid any rounding
                  // issues associated with floating point. 
    friend std::istream& operator>>(std::istream& s, Price& data)
    {
        return s >> data.units >> data.value;
    }
};

如何从字符串中提取浮点数？

How to extract floating point numbers from a string?

c++

string

fstream

数据线

ItemNameReader

DataBlob

价格