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LIBGRAPH(3)                                              LIBGRAPH(3)

       libgraph - abstract graph library

       #include <graphviz/graph.h>
       void        aginit();
       Agraph_t    *agread(FILE*);
       int         agwrite(Agraph_t*, FILE*);
       int         agerrors();
       Agraph_t    *agopen(char *name, int kind);
       void        agclose(Agraph_t *g);
       Agraph_t    *agsubg(Agraph_t *g, char *name);
       Agraph_t    *agfindsubg(Agraph_t *g, char *name);
       Agnode_t    *agmetanode(Agraph_t *g);
       Agraph_t    *agusergraph(Agnode_t *metanode);
       int         agnnodes(Agraph_t *g), agnedges(Agraph_t *g);
       int         agcontains(Agraph_t *g, void *obj);
       int         aginsert(Agraph_t *g, void *obj);
       int         agdelete(Agraph_t *g, void *obj);

       Agnode_t    *agnode(Agraph_t *g, char *name);
       Agnode_t    *agfindnode(Agraph_t *g, char *name);
       Agnode_t    *agfstnode(Agraph_t *g);
       Agnode_t    *agnxtnode(Agraph_t *g, Agnode_t *n);
       Agnode_t    *aglstnode(Agraph_t *g);
       Agnode_t    *agprvnode(Agraph_t *g, Agnode_t *n);

       Agedge_t    *agedge(Agraph_t *g, Agnode_t *tail, Agnode_t *head);
       Agedge_t    *agfindedge(Agraph_t *g, Agnode_t *tail, Agnode_t *head);
       Agedge_t    *agfstedge(Agraph_t *g, Agnode_t *n);
       Agedge_t    *agnxtedge(Agraph_t *g, Agedge_t *e, Agnode_t *n);
       Agedge_t    *agfstin(Agraph_t *g, Agnode_t *n);
       Agedge_t    *agnxtin(Agraph_t *g, Agedge_t *e);
       Agedge_t    *agfstout(Agraph_t *g, Agnode_t *n);
       Agedge_t    *agnxtout(Agraph_t *g, Agedge_t *e);

       char        *agget(void *obj, char *name);
       char        *agxget(void *obj, int index);
       void        agset(void *obj, char *name, char *value);
       void        agxset(void *obj, int index, char *value);
       int         agindex(void *obj, char *name);

       Agsym_t*    agraphattr(Agraph_t *g,char *name,char *value);
       Agsym_t*    agnodeattr(Agraph_t *g,char *name,char *value);
       Agsym_t*    agedgeattr(Agraph_t *g,char *name,char *value);
       Agsym_t*    agfindattr(void *obj,char *name);

       libgraph  maintains directed and undirected attributed graphs
       in memory and reads and writes graph files.  Graphs are  com‐
       posed of nodes, edges, and nested subgraphs.   A subgraph may
       contain any nodes and edges of its parents, and may be passed
       to  any  libgraph function taking a graph pointer, except the
       three that create new  attributes  (where  a  main  graph  is

       Attributes are internal or external.  Internal attributes are
       fields in the graph, node and edge structs defined at compile
       time.  These allow efficient representation and direct access
       to values such as marks, weights, and  pointers  for  writing
       graph  algorithms.   External  attributes, on the other hand,
       are character strings (name-value  pairs)  dynamically  allo‐
       cated at runtime and accessed through libgraph calls.  Exter‐
       nal  attributes  are  used  in  graph  file   I/O;   internal
       attributes are not.  Conversion between internal and external
       attributes must be explicitly programmed.

       The subgraphs in a main graph are represented by an auxiliary
       directed graph (a meta-graph).  Meta-nodes correspond to sub‐
       graphs, and meta-edges signify containment of one subgraph in
       another.   agmetanode  and  agusergraph map between subgraphs
       and meta-nodes.  The nodes and edges of the meta-graph may be
       traversed by the usual libgraph functions for this purpose.

       1.  Define types Agraphinfo_t, Agnodeinfo_t, and Agedgeinfo_t
       (usually    in    a    header    file)    before    including

       2.  Call aginit() before any other libgraph functions.  (This
       is a macro that calls aginitlib()  to  define  the  sizes  of
       Agraphinfo_t, Agnodeinfo_t, and Agedgeinfo_t.)

       3. Compile with -lgraph -lcdt.

       Except  for  the  u  fields, libgraph data structures must be
       considered read-only.  Corrupting their  contents  by  direct
       updates can cause catastrophic errors.

       typedef struct Agraph_t {
           char                 kind;
           char                *name;
           Agraph_t             *root;
           char                **attr;
           graphdata_t         *univ;
           Dict_t              *nodes,*inedges,*outedges;
           proto_t             *proto;
           Agraphinfo_t         u;
       } Agraph_t;

       typedef struct graphdata_t {
           Dict_t              *node_dict;
           attrdict_t          *nodeattr, *edgeattr, *globattr;
       } graphdata_t;

       typedef struct proto_t {
           Agnode_t            *n;
           Agedge_t            *e;
           proto_t             *prev;
       } proto_t;
       A  graph  kind is one of: AGRAPH, AGRAPHSTRICT, AGDIGRAPH, or
       AGDIGRAPHSTRICT.  There are related macros  for  testing  the
       properties of a graph: AG_IS_DIRECTED(g) and AG_IS_STRICT(g).
       Strict graphs cannot have self-arcs or multi-edges.  attr  is
       the  array of external attribute values.  univ points to val‐
       ues shared by all subgraphs of a main graph.  nodes, inedges,
       and  outedges  are  sets  maintained by cdt(3).  Normally you
       don't access these dictionaries  directly,  though  the  edge
       dictionaries  may be re-ordered to support programmer-defined
       ordered edges (see dtreorder in cdt(3)).  proto is a stack of
       templates  for  node and edge initialization.  The attributes
       of these nodes and edges are set in  the  usual  way  (agget,
       agset, etc.) to set defaults.

       agread  reads  a file and returns a new graph if one was suc‐
       cesfully parsed, otherwise returns NULL if EOF  or  a  syntax
       error  was  encountered.  Errors are reported on stderr and a
       count is returned  from  agerrors().   write_graph  prints  a
       graph  on  a  file.  agopen and agsubg create new empty graph
       and subgraphs.  agfindsubg searches for a subgraph  by  name,
       returning NULL when the search fails.

       agcontains,  aginsert,  agdelete  are  generic  functions for
       nodes, edges, and graphs.   gcontains  is  a  predicate  that
       tests  if  an  object  belongs  to the given graph.  aginsert
       inserts an object in a graph and agdelete undoes this  opera‐
       tion.  A node or edge is destroyed (and its storage freed) at
       the time it is deleted from the main graph.  Likewise a  sub‐
       graph is destroyed when it is deleted from its last parent or
       when its last parent is deleted.

       typedef struct Agnode_t {
           char                *name;
           Agraph_t            *graph;
           char                **attr;
           Agnodeinfo_t        u;
       } Agnode_t;

       agnode attempts to create a node.  If one with the  requested
       name  already  exists,  the  old node is returned unmodified.
       Otherwise a new node is created, with attributed copied  from
       g->proto->n.   agfstnode  (agnxtnode) return the first (next)
       element in the node set of a graph,  respectively,  or  NULL.
       aglstnode  (agprvnode)  return the last (previous) element in
       the node set of a graph, respectively, or NULL.

       typedef struct Agedge_t {
           Agnode_t            *head,*tail;
           char                **attr;
           Agedgeinfo_t        u;
       } Agedge_t;
       agedge creates a new edge with the attributes of  g->proto->e
       including  its  key if not empty.  agfindedge finds the first
       (u,v) edge in g.   agfstedge  (agnxtedge)  return  the  first
       (next)  element  in the edge set of a graph, respectively, or
       NULL.  agfstin, agnxtin, agfstout, agnxtout refer to  in-  or
       out-edge sets.  The idiomatic usage in a directed graph is:

           for   (e   =   agfstout(g,n);   e;  e  =  agnextout(g,e))

       An edge is uniquely identified by its endpoints and  its  key
       attribute  (if  there  are  multiple  edges).   If the key of
       g->proto->e is empty, new  edges  are  assigned  an  internal
       value.   Edges also have tailport and headport values.  These
       have special syntax in the graph file language  but  are  not
       otherwise interpreted.

       typedef struct attrsym_t {
           char                *name,*value;
           int                 index;
           unsigned char       printed;
       } attrsym_t;
       typedef struct attrdict_t  {
           char                *name;
           Dict_t              *dict;
           attrsym_t           **list;
       } attrdict_t;
       agraphattr,  agnodeattr,  and agedgeattr make new attributes.
       g should be a main graph, or NULL for  declarations  applying
       to  all  graphs  subsequently  read  or  created.  agfindattr
       searches for an existing attribute.

       External attributes are accessed by  agget  and  agset  These
       take  a pointer to any graph, node, or edge, and an attribute
       name.  Also, each attribute has an integer index.  For  effi‐
       ciency this index may be passed instead of the name, by call‐
       ing agxget and agxset.  The printed flag of an attribute  may
       be set to 0 to skip it when writing a graph file.

       The list in an attribute dictionary is maintained in order of
       creation and is NULL terminated.  Here is a program  fragment
       to print node attribute names:
           attrsym_t *aptr;
           for (i = 0; aptr = g->univ->nodedict->list[i]; i++) puts(aptr->name);

       graph any_name {            /* an undirected graph */
           a -- b;                 /* a simple edge */
           a -- x1 -- x2 -- x3;    /* a chain of edges */
           "x3.a!" -- a;           /* quotes protect special characters */
           b -- {q r s t};         /* edges that fan out */
           b [color="red",size=".5,.5"];   /* set various node attributes */
           node [color=blue];      /* set default attributes */
           b -- c [weight=25];     /* set edge attributes */
           subgraph sink_nodes {a b c};    /* make a subgraph */

       digraph G {
           size="8.5,11";            /* sets a graph attribute */
           a -> b;                 /* makes a directed edge */
           chip12.pin1 -> chip28.pin3; /* uses named node "ports" */

       dot(1), neato(1), libdict(3)
       S.  C.  North and K. P. Vo, "Dictionary and Graph Libraries''
       1993 Winter USENIX Conference Proceedings, pp. 1-11.

       Stephen North (,  AT&T  Bell  Laborato‐

                            01 MARCH 1993                LIBGRAPH(3)
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