Getting variables values from a .txt file in C++ - c++

Question

I am writing a CFD solver in C++ but I am in the very beginning. Now I am coding a solver for the linear convection. The math is ok, working well, but I need to write also a code for reading variables from a .txt file.
My code is:
//Code for solving the convection linear equation from Navier-Stokes
#include <iostream>
using namespace std;
int main()
{
float endtime=0.3; //simulation time
float dx=0.025; //element size
float xmax=2; //domain size
float c=1; //wave velocity
float C=0.3; //Courant-Friedrich-Lewy number
float dt=C*dx/c; //defining timestep by the Courant equantion
int nx=xmax/dx + 1; //defining number of elements
int nt=endtime/dt; //defining number of time points
float u[nx] = { }; //defining an initial velocity array.
float un[nx] = { };
for(int i = 4; i <= 9; i++) //defining contour conditions
{
u[i] = 2;
}
for(int n=1; n<=nt; n++)
{
std::copy(u, u + nx, un);
for(int i=1; i<=nx; i++)
{
u[i] = un[i] - c*(dt/dx)*(un[i]-un[i-1]);
}
}
for (int i = 0; i <= nx; i++)
{
cout << u[i] << endl;
}
return 0;
}
I need to take these variables values from a .txt, like the end time, element size, etc. Then, I have a .txt called "parameters", which is exactly written like that:
endtime=0.3
dx=0.025
xmax=2
c=1
C=0.3
What's the most effiecient way to get these variables values from this .txt and use it in the code?

Answer 1

Using only standard features:
#include <iostream>
#include <tuple>
using namespace std;
tuple<bool, string, string> read_one_value(istream& in)
{
string name;
if(getline(in, name, '='))
{
string value;
if(getline(in, value))
{
return make_tuple(true, name, value);
}
}
return make_tuple(false, "", "");
}
int main()
{
for(auto val = read_one_value(cin); get<0>(val); val = read_one_value(cin))
{
std::cout << get<1>(val) << " -> " << get<2>(val) << '\n';
}
return 0;
}
This leaves converting from the value string objects to the needed type as an exercise for the reader, and assumes your format of name=value is consistent.