how to plot graph using GNUplot in C++

Question

when I execute my program, I want my program to plot a graph and display on the screen. But I am not sure how do I do that. Here is the example C++ code.

#include "stdafx.h"
# include <cstdlib>
# include <iostream>
# include <iomanip>
# include <cmath>

using namespace std;

# include "curve_plot.h"

int main();  
int main()


{
    int i;
    int n;
    double *x;
    double *y;

    cout << "\n";
    cout << "CURVE_PLOT_PRB:\n";
    cout << "  Demonstrate how CURVE_PLOT can be used.\n";

    //  Set up some data to plot.

    n = 51;
    x = new double[n];
    y = new double[n];
    for (i = 0; i < 51; i++)
    {
        x[i] = (double)(i) / 10.0;
        y[i] = x[i] * cos(x[i]);
    }

    //  Send the data to curve_plot.
    curve_plot(n, x, y, "curve_plot");

    //  Free memory.


    delete[] x;
    delete[] y;



    return 0;
}

and here is the header file.

void curve_plot(int n, double x[], double y[], string name);

curve_plot.cpp

#include "stdafx.h"
# include <cstdlib>
# include <iostream>
# include <iomanip>
# include <fstream>
#include <string>
using namespace std;

# include "curve_plot.h"

void curve_plot(int n, double x[], double y[], string name)


{
    string command_filename;
    ofstream command_unit;
    string data_filename;
    ofstream data_unit;
    int i;
    string plot_filename;

    //  Write the data file.

    data_filename = name + "_data.txt";
    data_unit.open(data_filename.c_str());
    for (i = 0; i < n; i++)
    {
        data_unit << x[i] << "  "
            << y[i] << "\n";
    }
    data_unit.close();
    cout << "\n";
    cout << "  Plot data written to the file \"" << data_filename << "\".\n";

    //  Write the command file.

    command_filename = name + "_commands.txt";
    command_unit.open(command_filename.c_str());
    command_unit << "set term png\n";
    plot_filename = name + ".png";
    command_unit << "set output \"" << plot_filename << "\"\n";
    command_unit << "set grid\n";
    command_unit << "set style data lines\n";
    command_unit << "unset key\n";
    command_unit << "set xlabel '<---X--->'\n";
    command_unit << "set ylabel '<---Y--->'\n";
    command_unit << "set timestamp\n";
    command_unit << "plot \"" << data_filename << "\" using 1:2 with lines lw 3\n";
    command_unit << "quit\n";
    command_unit.close();
    cout << "  Command data written to \"" << command_filename << "\".\n";

    return;
}

user4489658 · Accepted Answer · 2016-12-01 18:54:41Z

1

What do you want, to run gnuplot from your C++ program or to run it after your C++ program execution? If it's the first, add

system("gnuplot gnuplot_command_file");

just before return statement. Of course, firstly you have to build a character string as a paramater of the system statement.

Otherwise, just execute in your command prompt

gnuplot your_command_file

answered Dec 1, 2016 at 18:54

user4489658

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4 Comments

Rick Over a year ago

to run the gnuplot from my C++ program. do i just build a character string and add system("gnuplot command_file"); I guess I will have to also add the Gnu plot header file?

user4489658 Over a year ago

gnuplot ist just a program that can be executed, from command line or from your program, So, yes.

Rick Over a year ago

so I did just as You mentioned, I run the code but still the graph does not get displayed though the program executes fine. P.S. : I am using visual studio 2015 to execute my programs

user4489658 Over a year ago

Graph doesn't get displayed because in the file curve_plot_commands.txt the terminal is set to png, so instead of showing the window, the file curve_plot.png is created. Comment the line containing set term png and instead of quit write pause mouse. For me, it works.

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