How to read float with scientific notation from file C++?

问题

I have a file with this format:

-0.0064785667 0.73900002 0.028505694 4.7858757e-39 315 218
-0.0051828534 0.73900002 0.028505694 4.6936954e-39 316 218
-0.0038818798 0.73799998 0.028467119 5.1546736e-39 317 218
-0.0025879198 0.73799998 0.028467119 5.6160217e-39 318 218
-0.0012939599 0.73799998 0.028467119 6.4461411e-39 319 218

I read it with this code:

using namespace std;   

ifstream inputFile;

//Opens data file for reading.
inputFile.open(filePath.c_str());

//Creates vector, initially with 0 points.
vector<Point> data(0);
float temp_x,temp_y,temp_z,rgb=0,discard_1=0,discard_2=0;

//Read contents of file till EOF.
while (inputFile.good()){

    inputFile >> temp_x >> temp_y >> temp_z >> rgb >> discard_1 >> discard_2;

    data.push_back(Point(temp_x,temp_y,temp_z,rgb));

}

if (!inputFile.eof())
    if (inputFile.fail()) cout << "Type mismatch during parsing." << endl;
    else cout << "Unknow problem during parsing." << endl;

//Close data file.
inputFile.close();

Reading the scientific notation float results in a type mismatch.

How can I read all the numbers including the scientific notation float?

回答1:

The problem is probably your while-loop. Never use while(inputFile.good()). Use this:

while (inputFile >> temp_x >> temp_y >> temp_z 
                 >> rgb >> discard_1 >> discard_2) {}

This answer to a different question explains why. You might also be interested in this answer, which suggests a more elegant solution.

回答2:

Expanding upon Björn Pollex's answer with an example without any error-handling:

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

struct point
{
    double x, y, z, rgb;
};

struct point_line: public point
{
    int discard[2];
};

std::istream& operator >>(std::istream& is, point_line& in)
{
    is >> in.x >> in.y >> in.z >> in.rgb >> in.discard[0] >> in.discard[1];
    // TODO: Add your error-handlin

    return is;
}

std::ostream& operator <<(std::ostream& os, const point& out)
{
    os << " X: " << out.x
       << " Y: " << out.y
       << " Z: " << out.z
       << " RGB: " << out.rgb
       ;

    return os;
}

int main()
{
    std::ifstream points_file("points.txt");
    std::vector<point> points;
    std::copy(std::istream_iterator<point_line>(points_file),
              std::istream_iterator<point_line>(),
              std::back_inserter(points));

    std::copy(points.begin(),
              points.end(),
              std::ostream_iterator<point>(std::cout, "\n"));
}

来源：https://stackoverflow.com/questions/8986488/how-to-read-float-with-scientific-notation-from-file-c

标签

c++

floating-point

iostream

scientific-notation