I have written a program which writes a list of data to a '.dat' file with the intention of then plotting it separately using gnuplot. Is there a way of making my code plot it automatically? My output is of the form:
x-coord analytic approximation
x-coord analytic approximation
x-coord analytic approximation
x-coord analytic approximation
x-coord analytic approximation
....
Ideally, when I run the code the graph would also be printed with an x-label, y-label and title (which could be changed from my C code). Many thanks.
To plot functions simply type: plot [function] at the gnuplot> prompt. Discrete data contained in a file can be displayed by specifying the name of the data file (enclosed in quotes) on the plot or splot command line. Data files should have the data arranged in columns of numbers.
An excellent C++ library to plot graphs is ROOT. It was developed by CERN for physicists. It also includes a C++ shell, in case you want to use C++ with an interactive prompt. You can find the documentation, download links, and lots of examples, at https://root.cern/.
I came across this while searching for something else regarding gnuplot. Even though it's an old question, I thought I'd contribute some sample code. I use this for a program of mine, and I think it does a pretty tidy job. AFAIK, this PIPEing only works on Unix systems (see the edit below for Windows users). My gnuplot installation is the default install from the Ubuntu repository.
#include <stdlib.h>
#include <stdio.h>
#define NUM_POINTS 5
#define NUM_COMMANDS 2
int main()
{
char * commandsForGnuplot[] = {"set title \"TITLEEEEE\"", "plot 'data.temp'"};
double xvals[NUM_POINTS] = {1.0, 2.0, 3.0, 4.0, 5.0};
double yvals[NUM_POINTS] = {5.0 ,3.0, 1.0, 3.0, 5.0};
FILE * temp = fopen("data.temp", "w");
/*Opens an interface that one can use to send commands as if they were typing into the
* gnuplot command line. "The -persistent" keeps the plot open even after your
* C program terminates.
*/
FILE * gnuplotPipe = popen ("gnuplot -persistent", "w");
int i;
for (i=0; i < NUM_POINTS; i++)
{
fprintf(temp, "%lf %lf \n", xvals[i], yvals[i]); //Write the data to a temporary file
}
for (i=0; i < NUM_COMMANDS; i++)
{
fprintf(gnuplotPipe, "%s \n", commandsForGnuplot[i]); //Send commands to gnuplot one by one.
}
return 0;
}
EDIT
In my application, I also ran into the problem that the plot doesn't appear until the calling program is closed. To get around this, add a fflush(gnuplotPipe)
after you've used fprintf
to send it your final command.
I've also seen that Windows users may use _popen
in place of popen
-- however I can't confirm this as I don't have Windows installed.
EDIT 2
One can avoid having to write to a file by sending gnuplot the plot '-'
command followed by data points followed by the letter "e".
e.g.
fprintf(gnuplotPipe, "plot '-' \n");
int i;
for (int i = 0; i < NUM_POINTS; i++)
{
fprintf(gnuplotPipe, "%lf %lf\n", xvals[i], yvals[i]);
}
fprintf(gnuplotPipe, "e");
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