Multiple graphs inside Graphviz DOT file - graphviz

Question

I have this Graphviz DOT graph:
digraph unit_test {
label="Unit test"
edge [fillcolor="#a6cee3" color="#1f78b4"]
node[shape="ellipse" style="filled" fillcolor="#1f77b4"]
start
end
node[shape="box" style="filled" fillcolor="#ff7f0e"]
process
subgraph cluster_process {
label = "Major logic"
process
}
start -> process
process -> end
}
The above renders as:
I have this second graph:
digraph details {
label = "Process details"
edge [fillcolor="#a6cee3" color="#1f78b4"]
node[shape="ellipse" style="filled" fillcolor="#1f77b4"]
start
end
node[shape="box" style="filled" fillcolor="#ff7f0e"]
details
subgraph cluster_details {
label = "Details"
details
}
start -> details
details -> end
}
Which renders to:
Problem
When I put the above two graphs inside the same DOT file named supporting.dot and I run dot -Tpng -o supporting.png supporting.dot command, terminal prints out some jiberish and the output image file won't contain both graphs, it just contains the first one. Is it possible to use multiple graphs inside a single DOT file? If so, what am I missing?

Answer 1

Question is unclear about what is to be accomplished, but maybe the following is a starting point
digraph G{
subgraph unit_test {
label="Unit test"
edge [fillcolor="#a6cee3" color="#1f78b4"]
node[shape="ellipse" style="filled" fillcolor="#1f77b4"]
start
end
node[shape="box" style="filled" fillcolor="#ff7f0e"]
process
subgraph cluster_process {
label = "Major logic"
process
}
start -> process
process -> end
}
subgraph details {
label = "Process details"
edge [fillcolor="#a6cee3" color="#1f78b4"]
node[shape="ellipse" style="filled" fillcolor="#1f77b4"]
start1 [label="start"]
end1 [label="end"]
node[shape="box" style="filled" fillcolor="#ff7f0e"]
details
subgraph cluster_details {
label = "Details"
details
}
start1 -> details
details -> end1
}
}
Note the naming / labels in the second subgraph.

Answer 2

Dot can't render 2 graphs into a single file, the output you see is probably the content of one of the graphs as a png.
In order to prevent that, you may run your graphs first through gvpack - something similar to:
gvpack -u supporting.dot | dot -Tpng -o supporting.png
This combines all graphs in supporting.dot into a single graph, which then is rendered with dot.
The layout of the graphs can be influenced by some more options of gvpack.

Answer 3

It is legal to have multiple graphs defined in one input file. You can then produce multiple output files using the -O option, like this:
dot -Tpng -O multi.gv
This will produce multi.gv.png and multi.gv.2.png

Answer 4

I got a better answer
http://www.bound-t.com/manuals/ref-manual.pdf
The -dot_dir option and the names of drawing files
The -dot option creates a single file that contains all drawings from one Bound-T run. If you
then use the dot tool to create a PostScript file, each drawing will go on its own page in the
PostScript file. However, dot can also generate graphical formats that do not have a concept of
"page" and then it may happen that only the first drawing is visible. If you want to use such
non-paged graphical formats it is better to create a directory (folder) to hold the drawing files
and use the Bound-T option -dot_dir instead of the option -dot. The -dot_dir option creates a
separate file for each drawing, named as follows:
• The call-graph of a root subprogram is put in a file called cg_R_nnn.dot, where R is the
link-name of the root subprogram, edited to replace most non-alphanumeric characters
with underscores '_', and nnn is a sequential number to distinguish root subprograms that
have the same name after this editing.
• If the call-graph of some root subrogram is recursive, Bound-T draws the joint call-graph of
all roots and puts it in a file called jcg_all_roots_001.dot.
• The flow-graph of a subprogram is put in a file called fg_S_nnn.dot, where S is the linkname of the subprogram, edited as above, and nnn is a sequential number to distinguish
subprograms that have the same name after this editing and also to distinguish drawings
that show different flow-graphs (execution bounds) for the same subprogram.
The sequential numbers nnn start from 1 and increment by 1 for each drawing file; the same
number sequence is shared by all types of drawings and all subprograms. For example, if we
analyse the root subprogram main?func that calls the two subprograms start$sense and
start$actuate, with the -dot_dir option and -draw options that ask for one flow-graph drawing
of each subprogram, the following drawing files are created:
• cg_main_func_001.dot for the call-graph of main?func
• fg_main_func_002.dot for the flow-graph of main?func
• fg_start_sense_003.dot for the flow-graph of start$sense
• fg_start_actuate_004.dot for the flow-graph of start$actuate.