How to pass a variable defined in C to Gnuplot through a pipe?

Question

I need to pass a variable defined in my main program (plain C) to Gnuplot through a pipe. How can I do so? Any assistance is greatly appreciated.

Thanks

PS: Ubuntu 12.04.3 LTS, GCC 4.6.3

The code:

FILE *pipe = popen("gnuplot -persist","w");
    //fprintf(pipe, "bin_width = binsize; ");
    fprintf(pipe, "load 'Q3.gnu' \n");
    close(pipe);

EDIT: I have solved my own problem, sorry to take your time. The solution is:

FILE *pipe = popen("gnuplot -persist","w");
    fprintf(pipe, "binsize = %f;", (float)binsize);
    fprintf(pipe, "load 'Q3.gnu' \n");
    close(pipe); 
    return 0;

Show your code. How does your C program communicate with gnuplot? What do you mean by passing a variable? Are you using popen ? How?? — Basile Starynkevitch
– Basile Starynkevitch, Commented Dec 22, 2013 at 22:58
@BasileStarynkevitch I am writing the part of the code relevant to my argument. — Vesnog
– Vesnog, Commented Dec 22, 2013 at 23:00
@BasileStarynkevitch The variable binsize is defined in my source C code and I want to pass it to Gnuplot and use it for plotting purposes. I commented out that part since it ran into problems, also I would opt for directly making it usable by Gnuplot without renaming it if possible. — Vesnog
– Vesnog, Commented Dec 22, 2013 at 23:03
If you mean shell pipe | then just print to stdout what you want to feed to gnuplot. Otherwise, clarify the question. — hyde
– hyde, Commented Dec 22, 2013 at 23:04
@hyde Please have a look at my edited post, I am using piping inside my C source file as I indicated. If the user changes the binsize defined at the start of the code this should be passes to Gnuplot. — Vesnog
– Vesnog, Commented Dec 22, 2013 at 23:05

Francisco Yepes Barrera · Accepted Answer · 2013-12-22 23:12:22Z

2

I can't give you an exact response, but gnuplot_i interface uses a pipe mechanism to comunicate with a gnuplot session. It seems very close to your request. I believe you can find useful information in the home page of the project (http://ndevilla.free.fr/gnuplot/).

answered Dec 22, 2013 at 23:12

Francisco Yepes Barrera

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1 Comment

Vesnog Over a year ago

Well thanks for your interest, I will have a look at the link you mentioned.

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