.de P0
.nf
\f5
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.fi
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.de Ss
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.TH LIBCGRAPH 3 "30 JULY 2007"
.SH "NAME"
\fBlibcgraph\fR \- abstract graph library
.SH "SYNOPSIS"
.\"ta .75i 1.5i 2.25i 3i 3.75i 4.5i 5.25i 6i
.PP
.nf
.P0
#include <graphviz/cgraph.h>
.P1
.SS "TYPES"
.P0
Agraph_t;
Agnode_t;
Agedge_t;
Agdesc_t;
Agdisc_t;
Agsym_t;
.P1
.SS "GRAPHS"
.P0
Agraph_t        *agopen(char *name, Agdesc_t kind, Agdisc_t *disc);
int             agclose(Agraph_t *g);
Agraph_t        *agread(void *channel, Agdisc_t *);
void			agreadline(int line_no);
void			agsetfile(char *file_name);
Agraph_t		*agconcat(Agraph_t *g, void *channel, Agdisc_t *disc)
int             agwrite(Agraph_t *g, void *channel);
int				agnnodes(Agraph_t *g),agnedges(Agraph_t *g);
int				agisdirected(Agraph_t * g),agisundirected(Agraph_t * g),agisstrict(Agraph_t * g), agissimple(Agraph_t * g); 
.SS "SUBGRAPHS"
.P0
Agraph_t        *agsubg(Agraph_t *g, char *name, int createflag);
Agraph_t		*agidsubg(Agraph_t * g, unsigned long id, int cflag);
Agraph_t        *agfstsubg(Agraph_t *g), agnxtsubg(Agraph_t *);
Agraph_t        *agparent(Agraph_t *g);
int				agdelsubg(Agraph_t * g, Agraph_t * sub);	/* same as agclose() */
.P1
.SS "NODES"
.P0
Agnode_t        *agnode(Agraph_t *g, char *name, int createflag);
Agnode_t        *agidnode(Agraph_t *g, ulong id, int createflag);
Agnode_t        *agsubnode(Agraph_t *g, Agnode_t *n, int createflag);
Agnode_t        *agfstnode(Agraph_t *g);
Agnode_t        *agnxtnode(Agraph_t *g, Agnode_t *n);
Agnode_t        *agprvnode(Agraph_t *g, Agnode_t *n);
Agnode_t        *aglstnode(Agraph_t *g);
int             agdelnode(Agraph_t *g, Agnode_t *n);
int				agdegree(Agnode_t *n, int use_inedges, int use_outedges);
.P1
.SS "EDGES"
.P0
Agedge_t        *agedge(Agraph_t* g, Agnode_t *t, Agnode_t *h, char *name, int createflag);
Agedge_t		*agidedge(Agraph_t * g, Agnode_t * t, Agnode_t * h, unsigned long id, int createflag);
Agedge_t        *agsubedge(Agraph_t *g, Agedge_t *e, int createflag);
Agnode_t        *aghead(Agedge_t *e), *agtail(Agedge_t *e);
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);
int             agdeledge(Agraph_t *g, Agedge_t *e);
.SS "STRING ATTRIBUTES"
.P0
Agsym_t			*agattr(Agraph_t *g, int kind, char *name, char *value);
Agsym_t			*agattrsym(void *obj, char *name);
Agsym_t			*agnxtattr(Agraph_t *g, int kind, Agsym_t *attr);
char			*agget(void *obj, char *name);
char			*agxget(void *obj, Agsym_t *sym);
int				agset(void *obj, char *name, char *value);
int				agxset(void *obj, Agsym_t *sym, char *value);
int				agsafeset(void *obj, char *name, char *value, char *def);
.P1
.SS "RECORDS"
.P0
void		*agbindrec(void *obj, char *name, unsigned int size, move_to_front);
Agrec_t     *aggetrec(void *obj, char *name, int move_to_front);
int         agdelrec(Agraph_t *g, void *obj, char *name);
int			agcopyattr(void *, void *);
void		aginit(Agraph_t * g, int kind, char *rec_name, int rec_size, int move_to_front);
void		agclean(Agraph_t * g, int kind, char *rec_name);
.P1
.SS "CALLBACKS"
.P0
Agcbdisc_t    *agpopdisc(Agraph_t *g);
void        agpushdisc(Agraph_t *g, Agcbdisc_t *disc);
void        agmethod(Agraph_t *g, void *obj, Agcbdisc_t *disc, int initflag);
.P1
.SS "MEMORY"
.P0
void		*agalloc(Agraph_t *g, size_t request);
void		*agrealloc(Agraph_t *g, void *ptr, size_t oldsize, size_t newsize);
void		agfree(Agraph_t *g, void *ptr);
.P1
.SS "STRINGS"
.P0
char		*agstrdup(Agraph_t *, char *);
char		*agstrdup_html(Agraph_t *, char *);
int		aghtmlstr(char *);
char		*agstrbind(Agraph_t * g, char *);
int		strfree(Agraph_t *, char *);
char		*agcanonStr(char *);
char		*agstrcanon(char *, char *);
.P1
.SS "GENERIC OBJECTS"
.P0
Agraph_t	*agraphof(void*);
Agraph_t	*agroot(void*);
int			agcontains(Agraph_t*, void*);
char		*agnameof(void*);
void		agdelete(Agraph_t *g, void *obj);
int 		agobjkind(void *obj);
Agrec_t		*AGDATA(void *obj);
ulong		AGID(void *obj);
int			AGTYPE(void *obj);
.P1
.SH "DESCRIPTION"
Libcgraph supports graph programming by maintaining graphs in memory
and reading and writing graph files.
Graphs are composed of nodes, edges, and nested subgraphs.
These graph objects may be attributed with string name-value pairs
and programmer-defined records (see Attributes).
.PP
All of Libcgraph's global symbols have the prefix \fBag\fR (case varying).
.SH "GRAPH AND SUBGRAPHS"
.PP
A ``main'' or ``root'' graph defines a namespace for a collection of
graph objects (subgraphs, nodes, edges) and their attributes.
Objects may be named by unique strings or by 32-bit IDs.
.PP
\fBagopen\fP creates a new graph with the given name and kind.
(Graph kinds are \fBAgdirected\fP, \fBAgundirected\fP,
\fBAgstrictdirected\fP, and \fBAgstrictundirected\fP.
A strict graph cannot have multi-edges or self-arcs.)
\fBagclose\fP deletes a graph, freeing its associated storage.
\fBagread\fP, \fBagwrite\fP, and \fBagconcat\fP perform file I/O 
using the graph file language described below. \fBagread\fP
constructs a new graph while \fBagconcat\fP merges the file
contents with a pre-existing graph.  Though I/O methods may
be overridden, the default is that the channel argument is
a stdio FILE pointer. \fBagsetfile\fP and \fBagreadline\fP
are helper functions that simply set the current file name
and input line number for subsequent error reporting.
.PP
\fBagsubg\fP finds or creates
a subgraph by name.  A new subgraph is is initially empty and
is of the same kind as its parent.  Nested subgraph trees may be created. 
A subgraph's name is only interpreted relative to its parent.
A program can scan subgraphs under a given graph
using \fBagfstsubg\fP and \fRagnxtsubg\fP.  A subgraph is
deleted with \fBagdelsubg\fP (or \fBagclose\fP).
.PP
By default, nodes are stored in ordered sets for efficient random
access to insert, find, and delete nodes.
The edges of a node are also stored in ordered sets.
The sets are maintained internally as splay tree dictionaries
using Phong Vo's cdt library.
.PP
\fBagnnodes\fP, \fBagnedges\fP, and \fBagdegree\fP return the
sizes of node and edge sets of a graph.  The \fBagdegree\fP returns
the size of the edge set of a nodes, and takes flags
to select in-edges, out-edges, or both.
.PP
An \fBAgdisc_t\fP defines callbacks to be invoked by libcgraph when
initializing, modifying, or finalizing graph objects.  (Casual users can ignore 
the following.) Disciplines are kept on a stack.  Libcgraph automatically
calls the methods on the stack, top-down.  Callbacks are installed
with \fBagpushdisc\fP, uninstalled with \fBagpopdisc\fP, and 
can be held pending or released via \fBagcallbacks\fP.
.PP
(Casual users may ignore the following.
When Libcgraph is compiled with Vmalloc (which is not the default),
each graph has its own heap.
Programmers may allocate application-dependent data within the
same heap as the rest of the graph.  The advantage is that
a graph can be deleted by atomically freeing its entire heap
without scanning each individual node and edge.
.SH "NODES"
A node is created by giving a unique string name or
programmer defined 32-bit ID, and is represented by a
unique internal object. (Node equality can checked
by pointer comparison.)
.PP
\fBagnode\fP searches in a graph or subgraph for a node
with the given name, and returns it if found.
If not found, if \fBcreateflag\fP is boolean true
a new node is created and returned, otherwise a nil
pointer is returned.
\fBagidnode\fP allows a programmer to specify the node
by a unique 32-bit ID.
\fBagsubnode\fP performs a similar operation on
an existing node and a subgraph.
.PP
\fBagfstnode\fP and \fBagnxtnode\fP scan node lists.
\fBagprvnode\fP and \fPaglstnode\fP are symmetric but scan backward.
The default sequence is order of creation (object timestamp.)
\fBagdelnode\fP removes a node from a graph or subgraph.
.SH "EDGES"
.PP
An abstract edge has two endpoint nodes called tail and head
where the all outedges of the same node have it as the tail
value and similarly all inedges have it as the head.
In an undirected graph, head and tail are interchangeable.
If a graph has multi-edges between the same pair of nodes,
the edge's string name behaves as a secondary key.
.PP
\fBagedge\fP searches in a graph of subgraph for an
edge between the given endpoints (with an optional
multi-edge selector name) and returns it if found.
Otherwise, if \fBcreateflag\fP is boolean true,
a new edge is created and returned: otherwise
a nil pointer is returned.  If the \fBname\fP 
is NULL, then an anonymous internal
value is generated. \fBagidedge\fP allows a programmer
to create an edge by giving its unique 32-bit ID.
\fBagfstin\fP, \fBagnxtint\fP, \fBagfstout\fP, and 
\fBagnxtout\fP visit directed in- and out- edge lists,
and ordinarily apply only in directed graphs.
\fBagfstedge\fP and \fBagnxtedge\fP visit all edges
incident to a node.  \fBagtail\fP and \fBaghead\fP
get the endpoint of an edge.
.SH "INTERNAL ATTRIBUTES"
Programmer-defined values may be dynamically
attached to graphs, subgraphs, nodes, and edges.
Such values are either uninterpreted binary records
(for implementing efficient algorithms)
or character string data (for I/O).
.SH "STRING ATTRIBUTES"
String attributes are handled automatically in reading
and writing graph files. 
A string attribute is identified by name and by
an internal symbol table entry (\fBAgsym_t\fP) created by Libcgraph.
Attributes of nodes, edges, and graphs (with their subgraphs)
have separate namespaces.  The contents of an \fBAgsym_t\fP
is listed below, followed by primitives to operate on string
attributes.
.P0
typedef struct Agsym_s {        /* symbol in one of the above dictionaries */
    Dtlink_t        link;
    char            *name;      /* attribute's name */
    char            *defval;    /* its default value for initialization */
    int             id;         /* its index in attr[] */
    unsigned char	kind;		/* referent object type */
    unsigned char	fixed;		/* immutable value */
} Agsym_t;
.P1
.PP
\fBagattr\fP creates or looks up attributes.
\fBkind\fP may be \fBAGRAPH\fP, \fBAGNODE\fP, or \fBAGEDGE\fP.
If \fBvalue\fP is \fB(char*)0)\fP, the request is to search
for an existing attribute of the given kind and name.
Otherwise, if the attribute already exists, its default
for creating new objects is set to the given value;
if it does not exist, a new attribute is created with the
given default, and the default is applied to all pre-existing
objects of the given kind. If \fBg\fP is NIL, the default is
set for all graphs created subsequently.
\fBagattrsym\fP is a helper function
that looks up an attribute for a graph object given as an argument.
\fBagnxtattr\fP permits traversing the list of attributes of
a given type.  If \fBNIL\fP is passed as an argument it gets
the first attribute, otherwise it returns the next one in
succession or returns \fBNIL\fP at the end of the list.
\fBagget\fP and \fPagset\fP allow fetching and updating a
string attribute for an object taking the attribute name as
an argument. \fBagxget\fP and \fBagxset\fP do this but with
an attribute symbol table entry as an argument (to avoid
the cost of the string lookup).  \fBagsafeset\fP is a
convenience function that ensures the given attribute is
declared before setting it locally on an object.

.SH "STRINGS"
Libcgraph performs its own storage management of strings as 
reference-counted strings.
The caller does not need to dynamically allocate storage.
.PP
\fBagstrdup\fP returns a pointer to a reference-counted copy of
the argument string, creating one if necessary. \fBagstrbind\fP
returns a pointer to a reference-counted string if it exists, or NULL if not.
All uses of cgraph strings need to be freed using \fBagstrfree\fP
in order to correctly maintain the reference count.
.PP
\fBagcanonStr\fP returns a pointer to a version of the input string
canonicalized for output for later re-parsing. This includes quoting
special characters and keywords. It uses its own internal buffer, so
the value will be lost on the next call to \fBagcanonStr\fP.
\fBagstrcanon\fP is an unsafe version of \fBagcanonStr\fP, in which
the application passes in a buffer as the second argument. Note that
the buffer may not be used; if the input string is in canonical form,
the function will just return a pointer to it.
.PP
The cgraph parser handles HTML-like strings. These should be 
indistinguishable from other strings for most purposes. To create
an HTML-like string, use \fBagstrdup_html\fP. The \fBaghtmlstr\fP
function can be used to query if a string is an ordinary string or
an HTML-like string.
.SH "RECORDS"
Uninterpreted records may be attached to graphs, subgraphs, nodes,
and edges for efficient operations on values such as marks, weights,
counts, and pointers needed by algorithms.  Application programmers
define the fields of these records, but they must be declared with
a common header as shown below.
.P0
typedef struct Agrec_s {
    Agrec_t		header;
    /* programmer-defined fields follow */
} Agrec_t;
.P1
Records are created and managed by Libcgraph. A programmer must
explicitly attach them to the objects in a graph, either to
individual objects one at a time via \fBagbindrec\fP, or to
all the objects of the same class in a graph via \fBaginit\fP.
(Note that for graphs, aginit is applied recursively to the
graph and its subgraphs if rec_size is negative (of the
actual rec_size.))
The \fBname\fP argument a record distinguishes various types of records,
and is programmer defined (Libcgraph reserves the prefix \fB_ag\fR).
If size is 0, the call to \fBagbindrec\fP is simply a lookup.
\fBagdelrec\fP is the deletes records one at a time.
\fBagclean\fP does the same for all objects of the same
class in an entire graph. 

Internally, records are maintained in circular linked lists
attached to graph objects.
To allow referencing application-dependent data without function
calls or search, Libcgraph allows setting and locking the list
pointer of a graph, node, or edge on a particular record.
This pointer can be obtained with the macro \fBAGDATA(obj)\fP.
A cast, generally within a macro or inline function,
is usually applied to convert the list pointer to
an appropriate programmer-defined type.

To control the setting of this pointer,
the \fBmove_to_front\fP flag may be \fBAG_MTF_FALSE\fP,
\fBAG_MTF_SOFT\fP, or \fBAG_MTF_HARD\fP accordingly.
The \fBAG_MTF_SOFT\fP field is only a hint that decreases
overhead in subsequent calls of \fBaggetrec\fP;
\fBAG_MTF_HARD\fP guarantees that a lock was obtained.
To release locks, use \fBAG_MTF_SOFT\fP or \fBAG_MTF_FALSE\fP.
Use of this feature implies cooperation or at least isolation
from other functions also using the move-to-front convention.

.SH "DISCIPLINES"
(The following is not intended for casual users.)
Programmer-defined disciplines customize certain resources-
ID namespace, memory, and I/O - needed by Libcgraph.
A discipline struct (or NIL) is passed at graph creation time.
.P0
struct Agdisc_s {			/* user's discipline */
	Agmemdisc_t			*mem;
	Agiddisc_t			*id;
	Agiodisc_t			*io;
} ;
.P1
A default discipline is supplied when NIL is given for
any of these fields.

An ID allocator discipline allows a client to control assignment
of IDs (uninterpreted 32-bit values) to objects, and possibly how
they are mapped to and from strings.

.P0
struct Agiddisc_s {		/* object ID allocator */
	void	*(*open)(Agraph_t *g);	/* associated with a graph */
	int		(*map)(void *state, int objtype, char *str, ulong *id, int createflag);
	int		(*alloc)(void *state, int objtype, ulong id);
	void	(*free)(void *state, int objtype, ulong id);
	char	*(*print)(void *state, int objtype, ulong id);
	void	(*close)(void *state);
} ;
.P1

\f5open\fP permits the ID discipline to initialize any data
structures that maintains per individual graph.
Its return value is then passed as the first argument to
all subsequent ID manager calls.

\f5alloc\fP informs the ID manager that Libcgraph is attempting
to create an object with a specific ID that was given by a client.
The ID manager should return TRUE (nonzero) if the ID can be
allocated, or FALSE (which aborts the operation).

\f5free\fP is called to inform the ID manager that the
object labeled with the given ID is about to go out of existence.

\f5map\fP is called to create or look-up IDs by string name
(if supported by the ID manager).  Returning TRUE (nonzero)
in all cases means that the request succeeded (with a valid
ID stored through \f5result\fP.  There are four cases:
.PP
\f5name != NULL\fP and \f5createflag == 1\fP:
This requests mapping a string (e.g. a name in a graph file) into a new ID.
If the ID manager can comply, then it stores the result and returns TRUE.
It is then also responsible for being able to \f5print\fP the ID again
as a string.  Otherwise the ID manager may return FALSE but it must
implement the following (at least for graph file reading and writing to work):
.PP
\f5name == NULL\fP and \f5createflag == 1\fP:
The ID manager creates a unique new ID of its own choosing. 
Although it may return FALSE if it does not support anonymous objects,
but this is strongly discouraged (to support "local names" in graph files.)
.PP
\f5name != NULL\fP and \f5createflag == 0\fP:
This is a namespace probe.  If the name was previously mapped into
an allocated ID by the ID manager, then the manager must return this ID.
Otherwise, the ID manager may either return FALSE, or may store
any unallocated ID into result. (This is convenient, for example,
if names are known to be digit strings that are directly converted into 32 bit values.)
.PP
\f5name == NULL\fP and \f5createflag == 0\fP: forbidden.
.PP
\f5print\fP is allowed to return a pointer to a static buffer;
a caller must copy its value if needed past subsequent calls.
\f5NULL\fP should be returned by ID managers that do not map names.
.PP
The \f5map\fP and \f5alloc\fP calls do not pass a pointer to the
newly allocated object.  If a client needs to install object
pointers in a handle table, it can obtain them via 
new object callbacks.
.P0
struct Agiodisc_s {
	int		(*fread)(void *chan, char *buf, int bufsize);
	int		(*putstr)(void *chan, char *str);
	int		(*flush)(void *chan);	/* sync */
	/* error messages? */
} ;

struct Agmemdisc_s {	/* memory allocator */
	void	*(*open)(void);		/* independent of other resources */
	void	*(*alloc)(void *state, size_t req);
	void	*(*resize)(void *state, void *ptr, size_t old, size_t req);
	void	(*free)(void *state, void *ptr);
	void	(*close)(void *state);
} ;
.P1

.SH "EXAMPLE PROGRAM"
.P0
#include <graphviz/cgraph.h>
typedef struct mydata_s {Agrec_t hdr; int x,y,z;} mydata;

main(int argc, char **argv)
{
    Agraph_t    *g;
    Agnode_t    *v;
    Agedge_t    *e;
    Agsym_t     *attr;
    Dict_t      *d
    int         cnt;
    mydata      *p;

    if (g = agread(stdin,NIL(Agdisc_t*))) {
		cnt = 0; attr = 0;
		while (attr = agnxtattr(g, AGNODE, attr)) cnt++;
		printf("The graph %s has %d attributes\n",agnameof(g),cnt);

		/* make the graph have a node color attribute, default is blue */
        attr = agattr(g,AGNODE,"color","blue");

        /* create a new graph of the same kind as g */
        h = agopen("tmp",g->desc);

        /* this is a way of counting all the edges of the graph */
        cnt = 0;
        for (v = agfstnode(g); v; v = agnxtnode(g,v))
            for (e = agfstout(g,v); e; e = agnxtout(g,e))
                cnt++;

        /* attach records to edges */
        for (v = agfstnode(g); v; v = agnxtnode(g,v))
            for (e = agfstout(g,v); e; e; = agnxtout(g,e)) {
                p = (mydata*) agbindrec(g,e,"mydata",sizeof(mydata),TRUE);
                p->x = 27;  /* meaningless data access example */
				((mydata*)(AGDATA(e)))->y = 999; /* another example */
        }
    }
}
.P1
.SH "EXAMPLE GRAPH FILES"
.P0
digraph G {
    a -> b;
    c [shape=box];
    a -> c [weight=29,label="some text];
    subgraph anything {
        /* the following affects only x,y,z */
        node [shape=circle];
        a; x; y -> z; y -> z;  /* multiple edges */
    }
}

strict graph H {
    n0 -- n1 -- n2 -- n0;  /* a cycle */
    n0 -- {a b c d};       /* a star */
    n0 -- n3;
    n0 -- n3 [weight=1];   /* same edge because graph is strict */
}
.P1
.SH "SEE ALSO"
Libcdt(3)

.SH "BUGS"
It is difficult to change endpoints of edges, delete string attributes or
modify edge keys.  The work-around is to create a new object and copy the
contents of an old one (but new object obviously has a different ID,
internal address, and object creation timestamp).

The API lacks convenient functions to substitute programmer-defined ordering of
nodes and edges but in principle this can be supported.
.SH "AUTHOR"
Stephen North, north@research.att.com, AT&T Research.