creating a pipe and writing to gnuplot terminal from c++

Question

I am trying to call the gnuplot from c++. I am using wgnuplot for Windows and VS2005 c++.

The following statement works because it opens the gnuplot terminal

FILE *p = _popen("wgnuplot -persist","w");

But I cannot write anything there. My terminal is still blank even after running the following code.

fprintf(p, "set terminal x11 enhanced\n"); //set appropriate output terminal for the plot 
fprintf(p, "set xlabel 'N'\n");//set xlabel 
fprintf(p, "set ylabel 'error'\n");//set ylabel

Could you please tell me what might be the problem, ie why the terminal is blank and fprintf() doesn't seem to work?

Thanks,

Boris

Answer 1

Check that FILE pointer is not NULL:

if(!p)
  // _popen() has failed...

Answer 2

I do not know if that helps you, but this is my approach of executing gnuplot from my C programs:

1. I create a template file (usually I do not delete it, so that it is easier to troubleshoot), where all the gnuplot commands are are scripted in.

2. I run gnuplot with

    system("gnuplot <TemplateFile>") 

If you are only interested in creating a plot, that his would do the job. If you are explicitly interested in the approach you described above then just disregard this posting ;)

Cherio Woltan