[rrd-users] Re: Error - ERROR: expected 2 data source readings (got 1) from a:a:...

Leif Neland leif at neland.dk
Tue Jul 12 21:33:15 MEST 2005

> Hi,
> I have written a very simple C program which will feed random data to
> the RRD tool for graphing. But, I am getting the error
> ERROR: expected 2 data source readings (got 1) from a:a:...
> My Create command is :
>    system("rrdtool create test_data.rrd --step 3 DS:a:GAUGE:600:0:U
> 5:1:200");
> In update, I would like to update the values of a and b with values 1
> and 2. Is this the right update command?
>    system("rrdtool update test_data.rrd a:1 b:2 N");
> If so, why am I getting an error?
The syntax is 
 rrdtool update filename
                --template|-t ds-name:ds-name:...

                at-time at value[:value...]

                [ time:value[:value...] ..]

In your case system("rrdtool update test_data.rrd N:1:2");
or, if you want to name your variables:
system("rrdtool update test_data.rrd -t a:b N:1:2");


> Also, what if I want to update a and b with not constants like 1, 2
> but with some value returned by a function say fn1() and fn2(). Is
> this how I write the update command?
>    ret1 = fn1();
>    ret2 = fn2();
>   system("rrdtool update test_data.rrd a:ret1 b:ret2 N");
> Is this ok? Please correct me.

system(sprintf("rrdtool update test_date.rrd N:%d:%d",ret1,ret2));

> Thanks!

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