[rrd-developers] Re: Wnat to use rrd into C

[Henrik Stoerner]

On Sat, Jul 08, 2006 at 02:12:38AM -0300, Rogério Schneider wrote:
> How can I create, update and graph directly from the C with RRD?
> Is there some include, lib, or some docs and samples of how to do this? I
> have read rrd.h but the prototypes is strange to me, and there is no
> documentation for C API.

The C API is basically just like the commandline API. E.g. to create a
graph you would run a command like

   rrdcreate myfile.rrd "DS:myval:GAUGE:600:0:U" "RRA:AVERAGE:0.5:1:576" 

In the C API, you'd just stick the commandline args into a char* table,
and pass them off to the appropriate function:

    char *createparams[] = {
       "rrdcreate",
       "myfile.rrd",
       "DS:myval:GAUGE:600:0:U",
       "RRA:AVERAGE:0.5:1:576",
       NULL
    };

    optind = opterr = 0; /* Because rrdtool uses getopt() */
    rrd_clear_error();
    rrd_create(4, createparams);


Likewise for an update - the command line is 

    rrdupdate myfile.rrd "0:42"

In C, that would be

    char *updateparams[] = {
       "rrdupdate",
       "myfile.rrd",
       "0:42",
       NULL
    };

    optind = opterr = 0;
    rrd_clear_error();
    rrd_update(3, updateparams);


rrd_graph works the same, but has some additional parameters that are
return values from the rrd_graph function. And this API changed from
rrdtool 1.0 -> 1.2. So what I do is like this:

    char **calcpr  = NULL;
    int rrdargcount, xsize, ysize, result;
    double ymin, ymax;
    char *rrdargs[] = {
        "rrdgraph",
	"mygraph.png",
	"-a", "PNG",
	"--title", "My Fancy Graph",
	"DEF:myval=myfile.rrd:myval:AVERAGE",
	"LINE2:myval#00CC00:The value",
	NULL
    };

    optind = opterr = 0;
    rrd_clear_error();
#ifdef RRDTOOL12
    result = rrd_graph(8, rrdargs, &calcpr, &xsize, &ysize, NULL, &ymin, &ymax);
#else
    result = rrd_graph(8, rrdargs, &calcpr, &xsize, &ysize);
#endif

    /* Was it OK ? */
    if (rrd_test_error() || (result != 0)) {
        if (calcpr) {
            int i;
            for (i=0; (calcpr[i]); i++) free(calcpr[i]);
            calcpr = NULL;
        }

	printf("Graph error: %s\n", rrd_get_error());
    }


I've snipped all of these code samples from the RRD handling code in my
monitoring toolkit - feel free to grab the full source from
hobbitmon.sourceforge.net.


Regards,
Henrik

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