I am trying to make strings into doubles using the values that I obtained from a .txt file.
The doubles I am obtaining have no decimals. I believe that this is because, in the .txt, the decimals of the numbers are separated by a comma instead of a dot. But I don't know how to solve that.
This is a simplification of my code:
#include <iostream>
#include <fstream> // read text file
#include <stdlib.h> // strtod, atof
int main() {
std::ifstream readWindData("winddata.txt");
// check that document has been opened correctly
if (!readWindData.is_open()) {
std::cout << "Wind data could not be opened." << std::endl;
return 1;
}
// skip headers of the table
std::string firstLine;
std::getline(readWindData, firstLine);
int numberOfRows = 0; // variable to count rows of the table
// initialise strings that separate each value
std::string time, string u10st, u40st, u60st, u80st, u100st,
u116st, u160st, dir10st, dir60st, dir100st, timeDecst;
// initialise doubles
double u10, u40, u60, u80, u100, u116, u160, dir10, dir60, dir100, timeDec;
std::string nextLine;
// Read strings and turn it into doubles line by line until end
while (readWindData >> time >> u10st >> u40st >> u60st >> u80st >> u100st
>> u116st >> u160st >> dir10st >> dir60st >> dir100st >> timeDecst) {
// try two different functions to turn strings into doubles:
u10 = strtod(u10st.c_str(), NULL);
u40 = atof(u40st.c_str());
// ensure numbers are displaying all their decimals
std::cout.precision(std::numeric_limits<double>::digits10 + 1);
// see what I am getting
std::cout << time << " " << u10st << " " << u10 << " " << u40 << "\n";
std::getline(readWindData, nextLine); // this line skips some crap on the side of some rows
numberOfRows++; // counts rows
}
std::cout << "Number of rows = " << numberOfRows << "\n";
readWindData.close();
return 0;
}
these are three lines of the file:
time (hour) u10(m/s)u40(m/s)u60 (m/s)u80(m/s)u100(m/s)u116(Um/s)u160(m/s)dir10 dir60 dir100 time decimal hours
00:00 4,25636 7,18414 8,56345 9,75567 10,9667 12,1298 13,8083 110,616 131,652 141,809 0 midnight
00:10 4,54607 7,40763 8,62832 9,91782 11,2024 12,2694 14,1229 114,551 133,624 142,565 0,166666667
And these are those lines outputted with the above code: (reminder, I std::cout time (string), u10st (string), u10 (double), u40 (double)).
00:00 4,25636 4 7
00:10 4,54607 4 7
Any ideas on how to read that 4,25636 string into a double 4.25636? The file is too long to modify.
To avoid messing around with the global locale you can just replace ,
with .
before calling strtod()
std::replace(u10st.begin(), u10st.end(), ',', '.');
u10 = strtod(u10st.c_str(), nullptr);
But in the program shown above you can also read from ifstream
directly into double
using operator >>
, if you use a locale where comma is a decimal separator.
readWindData.imbue(std::locale("de_DE.UTF-8")); // or fr, nl, ru, etc.
double u10, u40, u60, u80, u100, u116, u160, dir10, dir60, dir100, timeDec;
while (readWindData >> time >> u10 >> u40 >> u60 >> u80 >> u100
>> u116 >> u160 >> dir10 >> dir60 >> dir100 >> timeDec) {