NAME¶
libcgraph - abstract graph library
SYNOPSIS¶
#include <graphviz/cgraph.h>
TYPES¶
Agraph_t;
Agnode_t;
Agedge_t;
Agdesc_t;
Agdisc_t;
Agsym_t;
GRAPHS¶
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);
SUBGRAPHS¶
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() */
NODES¶
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);
EDGES¶
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);
STRING ATTRIBUTES¶
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);
RECORDS¶
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);
CALLBACKS¶
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);
MEMORY¶
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);
STRINGS¶
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 *);
GENERIC OBJECTS¶
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);
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).
All of Libcgraph's global symbols have the prefix
ag (case varying).
GRAPH AND SUBGRAPHS¶
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.
agopen creates a new graph with the given name and kind. (Graph kinds are
Agdirected,
Agundirected,
Agstrictdirected, and
Agstrictundirected. A strict graph cannot have multi-edges or
self-arcs.)
agclose deletes a graph, freeing its associated storage.
agread,
agwrite, and
agconcat perform file I/O using the
graph file language described below.
agread constructs a new graph
while
agconcat 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.
agsetfile and
agreadline are helper
functions that simply set the current file name and input line number for
subsequent error reporting.
agsubg 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
agfstsubg and
agnxtsubg. A subgraph is deleted with
agdelsubg (or
agclose).
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.
agnnodes,
agnedges, and
agdegree return the sizes of node
and edge sets of a graph. The
agdegree returns the size of the edge set
of a nodes, and takes flags to select in-edges, out-edges, or both.
An
Agdisc_t 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
agpushdisc, uninstalled with
agpopdisc, and can be held pending
or released via
agcallbacks.
(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.
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.)
agnode searches in a graph or subgraph for a node with the given name,
and returns it if found. If not found, if
createflag is boolean true a
new node is created and returned, otherwise a nil pointer is returned.
agidnode allows a programmer to specify the node by a unique 32-bit ID.
agsubnode performs a similar operation on an existing node and a
subgraph.
agfstnode and
agnxtnode scan node lists.
agprvnode and
aglstnode are symmetric but scan backward. The default sequence is
order of creation (object timestamp.)
agdelnode removes a node from a
graph or subgraph.
EDGES¶
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.
agedge 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
createflag is boolean true, a new edge is created and
returned: otherwise a nil pointer is returned. If the
name is NULL,
then an anonymous internal value is generated.
agidedge allows a
programmer to create an edge by giving its unique 32-bit ID.
agfstin,
agnxtint,
agfstout, and
agnxtout visit directed in- and
out- edge lists, and ordinarily apply only in directed graphs.
agfstedge and
agnxtedge visit all edges incident to a node.
agtail and
aghead get the endpoint of an edge.
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).
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
(
Agsym_t) created by Libcgraph. Attributes of nodes, edges, and graphs
(with their subgraphs) have separate namespaces. The contents of an
Agsym_t is listed below, followed by primitives to operate on string
attributes.
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;
agattr creates or looks up attributes.
kind may be
AGRAPH,
AGNODE, or
AGEDGE. If
value is
(char*)0), 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
g is NIL, the default is set for all
graphs created subsequently.
agattrsym is a helper function that looks
up an attribute for a graph object given as an argument.
agnxtattr
permits traversing the list of attributes of a given type. If
NIL is
passed as an argument it gets the first attribute, otherwise it returns the
next one in succession or returns
NIL at the end of the list.
agget and
agset allow fetching and updating a string attribute
for an object taking the attribute name as an argument.
agxget and
agxset do this but with an attribute symbol table entry as an argument
(to avoid the cost of the string lookup).
agsafeset is a convenience
function that ensures the given attribute is declared before setting it
locally on an object.
STRINGS¶
Libcgraph performs its own storage management of strings as reference-counted
strings. The caller does not need to dynamically allocate storage.
agstrdup returns a pointer to a reference-counted copy of the argument
string, creating one if necessary.
agstrbind 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
agstrfree in order to correctly maintain
the reference count.
agcanonStr 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
agcanonStr.
agstrcanon is an unsafe
version of
agcanonStr, 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.
The cgraph parser handles HTML-like strings. These should be indistinguishable
from other strings for most purposes. To create an HTML-like string, use
agstrdup_html. The
aghtmlstr function can be used to query if a
string is an ordinary string or an HTML-like string.
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.
typedef struct Agrec_s {
Agrec_t header;
/* programmer-defined fields follow */
} Agrec_t;
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
agbindrec, or to all the objects of the same class in a graph
via
aginit. (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
name argument a record distinguishes various types of records, and is
programmer defined (Libcgraph reserves the prefix
_ag). If size is 0,
the call to
agbindrec is simply a lookup.
agdelrec is the
deletes records one at a time.
agclean 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
AGDATA(obj). 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
move_to_front flag may be
AG_MTF_FALSE,
AG_MTF_SOFT, or
AG_MTF_HARD accordingly.
The
AG_MTF_SOFT field is only a hint that decreases overhead in
subsequent calls of
aggetrec;
AG_MTF_HARD guarantees that a lock
was obtained. To release locks, use
AG_MTF_SOFT or
AG_MTF_FALSE.
Use of this feature implies cooperation or at least isolation from other
functions also using the move-to-front convention.
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.
struct Agdisc_s { /* user's discipline */
Agmemdisc_t *mem;
Agiddisc_t *id;
Agiodisc_t *io;
} ;
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.
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);
} ;
open 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.
alloc 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).
free is called to inform the ID manager that the object labeled with the given
ID is about to go out of existence.
map 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 result. There are four cases:
name != NULL and createflag == 1: 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 print
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):
name == NULL and createflag == 1: 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.)
name != NULL and createflag == 0: 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.)
name == NULL and createflag == 0: forbidden.
print is allowed to return a pointer to a static buffer; a caller must copy its
value if needed past subsequent calls. NULL should be returned by ID managers
that do not map names.
The map and alloc 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.
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);
} ;
EXAMPLE PROGRAM¶
#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 attributes0,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 */
}
}
}
EXAMPLE GRAPH FILES¶
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 */
}
SEE ALSO¶
Libcdt(3)
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.
AUTHOR¶
Stephen North, north@research.att.com, AT&T Research.