Making C code plot a graph automatically - c

Question

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.

Answer 1

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");

Answer 2

You can either create a gnuplot script and spawn a process running gnuplot to plot this script from the commandline, or you may use one of the provided interfaces. For C, there is a POSIX pipe-based interface from Nicolas Devillard available here:
http://ndevilla.free.fr/gnuplot/
...and an iostream-based C++ version is available via git (see: http://www.stahlke.org/dan/gnuplot-iostream/ )
The most portable and probably the easiest way would still be calling gnuplot to plot a script, though. As sje397 mentioned, check your documentation for the system() call in stdlib.h.
On a sidenote, there is also GNU plotutils, which offers libplot, a library for plotting datasets, which you could use in your application. See: http://www.gnu.org/software/plotutils/

Answer 3

Although I've seen a lot of ways of doing this, the most simplest way of doing this would be by using the system() (from stdlib.h) function in C.
First make a gnuplot script and save it as "name.gp" (neither the name nor the extension matter).
A simple script would be,
plot 'Output.dat' with lines
After saving this script file, just add
system("gnuplot -p name.gp");
at the end of your code.
It's as simple as that.
Make sure to add gnuplot path to the Windows System Path variables.

Answer 4

I've adapted the accepted answer to plot a float array while avoiding the use of a temporary file. In it, float* data_ is the array and size_t size_ its size. Hopefully it is helpful for someone!
Cheers,
Andres
void plot(const char* name="FloatSignal"){
// open persistent gnuplot window
FILE* gnuplot_pipe = popen ("gnuplot -persistent", "w");
// basic settings
fprintf(gnuplot_pipe, "set title '%s'\n", name);
// fill it with data
fprintf(gnuplot_pipe, "plot '-'\n");
for(size_t i=0; i<size_; ++i){
fprintf(gnuplot_pipe, "%zu %f\n", i, data_[i]);
}
fprintf(gnuplot_pipe, "e\n");
// refresh can probably be omitted
fprintf(gnuplot_pipe, "refresh\n");
}

Answer 5

I know it's too late, but answering if it may help someone.
fputs really does the job, you want. first you need to print the data you want to plot in a temporary file data.temp.
FILE *pipe_gp = popen("gnuplot -p", "w");
fputs("set terminal png \n",pipe_gp);
fputs("set output 'abc.png' \n",pipe_gp);
fputs("set xlabel 'f' \n",pipe_gp);
fputs("set xrange [0:100] \n",pipe_gp);
fputs("set yrange [0:100] \n",pipe_gp);
fputs("plot 'data.temp' u 1:2 w circles lc rgb 'pink' notitle \n",pipe_gp);
pclose(pipe_gp);