c++ - C++中如何读取文件

Question

我正在尝试从名为“parking.txt”的文件中读取数据，我想从该文件中读取某些值并将它们输出到屏幕上。如何才能做到这一点？这能做到吗？

parking.txt 中的值为:

total 5
One 400
Five 300
Ten 200
Twenty 50
Quarter 500

在我的代码中，我想用文件中的适当值替换“line”。

#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

int main()
{
    ifstream inputFile ("parking_account.txt");
    string line;

    getline(inputFile, line);

    cout <<"\n\t-------------------------------------------------------";
    cout <<"\n\t=======================================================";
    cout <<"\n\t              Parking Machine Accounts                 ";
    cout <<"\n\t=======================================================";
    cout <<"\n\tSr. No.  : Bill Name       :  Bill Count  :  Cost(in$) ";
    cout <<"\n\t-------------------------------------------------------";
    cout <<"\n\t       1 : One Dollar      :  " << line << "  :  ";
    cout <<"\n\t       2 : Five Dollar     :  " << line << "  :  ";
    cout <<"\n\t       3 : Ten Dollar      :  " << line << "  :  ";
    cout <<"\n\t       4 : Twenty Dollar   :  " << line << "  :  ";
    cout <<"\n\t       5 : Quarter         :  " << line << "  :  ";

    cout<<"\n\tTotal bill types found : " <<line <<endl;
}

我尝试了一个逐行搜索的 while 循环，但它输出了 5 个相同的菜单，其中的行更新了该文本值。这是 while 循环。

int main()
{
    ifstream inputFile ("parking_account.txt");
    string line;

    getline(inputFile, line);
    while (inputFile)
    {
        cout <<"\n\t-------------------------------------------------------";
        cout <<"\n\t=======================================================";
        cout <<"\n\t              Parking Machine Accounts                 ";
        cout <<"\n\t=======================================================";
        cout <<"\n\tSr. No.  : Bill Name       :  Bill Count  :  Cost(in$) ";
        cout <<"\n\t-------------------------------------------------------";
        cout <<"\n\t       1 : One Dollar      :  " << line << "  :  ";
        cout <<"\n\t       2 : Five Dollar     :  " << line << "  :  ";
        cout <<"\n\t       3 : Ten Dollar      :  " << line << "  :  ";
        cout <<"\n\t       4 : Twenty Dollar   :  " << line << "  :  ";
        cout <<"\n\t       5 : Quarter         :  " << line << "  :  ";

        cout<<"\n\tTotal bill types found : " <<line <<endl;
        getline(inputFile, line);
    }
}

Answer 1

尝试使用提取运算符 >> :

string dummy; //this holds those separators since I have assumed that the numbers are always in the same order
//alternately, you could extract this two `>>`'s at a time, processing the string that
//comes befor the number to determine where it should go. For simplicity, I have
//assumed that the order is always the same.

int total one, five, ten, twenty, quarter;
inputFile >> dummy >> total >> dummy >> one >> dummy >> five >> dummy >> ten >> dummy >> twenty >> dummy >> quarter;

这是首先将“Total”字符串提取到 dummy 中.接下来，它将值“5”提取到整数 total 中。 .之后，它将“一”提取到dummy中。 , 400 入 one作为一个整数，“二”变成dummy , "300"变成five作为一个整数，等等。如果我误解了您的字符串格式，修改上面的内容应该很简单。

然后您可以替换您的 line输出中的变量，适当的变量保存您对表格感兴趣的值( one 、 five 等)。

>>运算符由 istream 提供并且对这些场景很有用。 (值得注意的是，这对 cin 也有效，因为 cin 的类是从 istream 派生的，就像 ifstream 是从 istream 派生的一样)