在C ++中读取Fortran数据类型

Question

I have a .txt containing data in Fortran datatypes. I am able to read the data using Python in the following manner.

import  fortranformat as ff

.....#more code in between.
with open(sys.argv[1]) as fh
.....#more code in between.  
    nodeline = ff.FortranRecordReader("(I3,I10,3E12.5)")
    line = fh.readline()
    data = nodeline.read(line)
#note that all the code is not provided.

I was wondering if there was a way to read Fortran datatypes from C++ (without using the function substring) from the .txt file.

PS. I have not provided the complete python code because it works properly and I am only using the bit required to explain my question better.

A sample of the data in the .txt file is given below.

 -1         1-3.07500E+01-2.96893E+01-1.65000E+01
 -1         2-3.07500E+01 2.96893E+01-1.65000E+01
 -1         3-8.85000E+01 8.74393E+01-1.65000E+01
 -1         4-8.85000E+01-8.74393E+01-1.65000E+01
 -1         5-8.85000E+01 8.74393E+01-2.15000E+01
 -1         6-8.85000E+01-8.74393E+01-2.15000E+01
 -1         7-3.07500E+01 2.96893E+01-2.15000E+01
 -1         8-3.07500E+01-2.96893E+01-2.15000E+01
 -1         9 2.96893E+01-3.07500E+01-1.65000E+01
 -1        10-2.96893E+01-3.07500E+01-1.65000E+01
 -1        11-8.74393E+01-8.85000E+01-1.65000E+01

Answer 1

Using the format provided in the question, I wrote a simple Fortran program to write some data.

      PROGRAM TEST
      WRITE(*,FMT='(I3,I10,3E12.5)') 1, 234, 5.67, 8.9, 0.123456789
      END PROGRAM

I piped the output of the above program to a file test.dat :

  1       234 0.56700E+01 0.89000E+01 0.12346E+00

Then in C++ the data can easily be read in using std::ifstream .

#include <fstream>
#include <iostream>

int main() {
    std::ifstream ifs("test.dat");

    int i,j;
    double d,e,f;

    while (ifs >> i >> j >> d >> e >> f) {
        std::cout << i << ' ' << j << ' ' << d << ' ' << e << ' ' << f << '\n';
    }
}

Compiling and running outputs

1 234 5.67 8.9 0.12346

---

Answer to the edit:

If you have to parse such a weird format where spaces are missing, you might want to consider using a proper parser generator such as Boost.Spirit.

#include <fstream>
#include <iostream>
#include <tuple>
#include <vector>

#include <boost/fusion/adapted/std_tuple.hpp>
#include <boost/spirit/home/support/iterators/istream_iterator.hpp>
#include <boost/spirit/home/x3.hpp>

int main() {
    std::ifstream input("test.dat");
    input.unsetf(std::ios::skipws);
    std::vector<std::tuple<int, int, double, double, double>> entries;

    boost::spirit::istream_iterator first(input);
    boost::spirit::istream_iterator last;

    using namespace boost::spirit::x3;

    bool r = phrase_parse(first, last,
                          *(int_ >> int_ >> double_ >> double_ >> double_),
                          space, entries);

    if (!r || first != last) {
        std::cerr << "Parsing failed at " << std::string{first, last} << '\n';
    } else {
        for (auto const &entry : entries) {
            int i, j;
            double d, e, f;
            std::tie(i, j, d, e, f) = entry;
            std::cout << i << ' ' << j << ' ' << d << ' ' << e << ' ' << f
                      << '\n';
        }
    }
}