跳过从数据文件C ++读取字符 [英] Skip reading characters from a data file C++

问题描述

我有一个具有以下格式的数据文件(A.dat):

I have a data file (A.dat) with following format:

Theta = 0.0000        Phi = 0.00000
Theta = 1.0000        Phi = 90.0000
Theta = 2.0000        Phi = 180.0000
Theta = 3.0000        Phi = 360.0000

我想读取(仅)theta和phi的值，并将它们存储在数据文件(B.dat)中，如下所示:

I want to read the values (only) of theta and phi and store them in a data file (B.dat) like this:

0.0000        0.00000
1.0000        90.0000
2.0000        180.0000
3.0000        360.0000

我尝试过这个:

    int main()
    {

      double C[4][2];

      ifstream fR;
      fR.open("A.dat");
      if (fR.is_open())
        {
          for(int i = 0; i<4; i++)
            fR >> C[i][0] >> C[i][1];  
        }
      else cout << "Unable to open file to read" << endl;
      fR.close();

      ofstream fW;
      fW.open("B.dat");

      for(int i = 0; i<4; i++)
        fW << C[i][0] << '\t' << C[i][1] << endl;

      fW.close();
    }

我在B.dat中得到了这个

I get this in B.dat:

0       6.95272e-310
6.95272e-310    6.93208e-310
1.52888e-314    2.07341e-317
2.07271e-317    6.95272e-310

如何跳过阅读字符和其他内容，只保存数字?

How do I skip reading characters and other things and save only the digits?

推荐答案

我经常使用 std :: getline 跳过过去不需要的数据，因为它允许您读取(并过去)特定字符(在本例中为'='):

I often use std::getline to skip past unwanted data because it allows you to read up to (and past) a specific character (in this case the '='):

#include <string>
#include <sstream>
#include <iomanip>
#include <iostream>

// pretend file stream
std::istringstream data(R"(
Theta = 0.0000        Phi = 0.00000
Theta = 1.0000        Phi = 90.0000
Theta = 2.0000        Phi = 180.0000
Theta = 3.0000        Phi = 360.0000
)");

int main()
{

    double theta;
    double phi;
    std::string skip; // used to read past unwanted text

    // set printing format to 4 decimal places
    std::cout << std::fixed << std::setprecision(4);

    while( std::getline(data, skip, '=')
        && data >> theta
        && std::getline(data, skip, '=')
        && data >> phi
    )
    {
        std::cout << '{' << theta << ", " << phi << '}' << '\n';
    }
}

输出:

{0.0000, 0.0000}
{1.0000, 90.0000}
{2.0000, 180.0000}
{3.0000, 360.0000}

注意:

我将阅读陈述放在 while()条件内.之所以可行，是因为从 stream 中读取将返回 stream 对象，并将其放入 if()或 while()条件，如果读取成功，则返回 true ，如果读取失败，则返回 false .

I put the reading statements inside the while() condition. This works because reading from a stream returns the stream object and when put into an if() or a while() condition it returns true if the read was successful or false if the read failed.

因此，当数据用完时，循环终止.

So the loop terminates when you run out of data.

这篇关于跳过从数据文件C ++读取字符的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！