从特定行开始将文件读取为成对向量

Question

Here is a txt file snippet that I have which lists temperature, voltage, and sensitivity

Temp.      Voltage    Sensitivity
(Kelvin)   (Volts)    (milliVolts/Kelvin)

1.4     1.644290        -12.5
1.5     1.642990        -13.6
1.6     1.641570        -14.8
1.7     1.640030        -16.0
1.8     1.638370        -17.1

What I am trying to accomplish is reading the values for Temp and Voltage into a vector of pairs, so that if looked up the Temp, I can find the corresponding Voltage. Would it be easier/more efficient to make two separate vectors and just look up the corresponding value based on its position?

void Convert::readFile()
{
    ifstream inFile;
    vector<double> temp,voltage;
    double kelvin,mV;

    inFile.open("DT-670.txt");
    if (inFile) {
        cout << "File Open";

        while(inFile>>kelvin && inFile>> mV)
        {
            temp.push_back(kelvin);
            voltage.push_back(mV);
        }

        cout<<temp.size();

    }

Answer 1

Here is the example code, you can change the line number and include conditional execution

#include <fstream>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>

using namespace std;

int main() {
  ifstream file("data.txt");
  string str = "";
  string::size_type sz;

  uint32_t line_number = 4;

  while (std::getline(file, str)) {
    cout << str << endl;

    istringstream buf(str);
    istream_iterator<string> beg(buf), end;

    vector<string> tokens(beg, end);

    for (auto &s : tokens)
      cout << atof(s.c_str()) << " " << flush;

    cout << endl;
  }
}

Answer 2

If you are not going to use the sensitivity data, you could do something like this:

std::map<double, double> table;
//...
double temperature = 0.0;
double voltage = 0.0;
double sensitivity = 0.0;
while (file >> temperature >> voltage >> sensitivity)
{
  table[temp] = voltage;
}

There is an fundamental issue here of using a floating point value as the search key. Floating point values, by their internal representation, can't be represented exactly; thus operator== may not work correctly for all values.

To get around the equality issue, most programs use an equivalence or epsilon to determine equality. For example, if the difference between two floating point values is less than 1E-6, consider them equal. I recommend exploring std::map to see how to overload the comparison operator (or provide a function for comparing values).