Plotting with gnuplot

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Section 30.1 Plotting with gnuplot

gnuplot is a command-line plotting program. Rather than writing data to a file and opening gnuplot separately, we can open a pipe directly to gnuplot from within our C program using popen(), then write gnuplot commands and data to that pipe with fprintf(), exactly as if we were writing to a file:

FILE *gfile = popen("gnuplot", "w");
fprintf(gfile, "set terminal png\n");
fprintf(gfile, "set output 'my_plot.png'\n");
fprintf(gfile, "plot '-'\n");        /* '-' means: data follows inline */
/* ... write x,y pairs, one per line ... */
fprintf(gfile, "e\n");               /* 'e' ends the inline data       */
pclose(gfile);

Here is a complete, minimal example that plots a single array of data points:

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We can plot multiple curves on the same figure, and add titles and axis labels, by extending the gnuplot commands we send through the pipe:

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