LIBCGRAPH(3)LIBCGRAPH(3)NAME
libcgraph - abstract graph library
SYNOPSIS
#include <graphviz/cgraph.h>
TYPES
Agraph_t;
Agnode_t;
Agedge_t;
Agdesc_t;
Agdisc_t;
Agsym_t;
Agrec_t;
Agcbdisc_t;
GLOBALS
Agmemdisc_t AgMemDisc;
Agiddisc_t AgIdDisc;
Agiodisc_t AgIoDisc;
Agdisc_t AgDefaultDisc;
GRAPHS
Agraph_t *agopen(char *name, Agdesc_t kind, Agdisc_t *disc);
int agclose(Agraph_t *g);
Agraph_t *agread(void *channel, Agdisc_t *);
Agraph_t *agmemread(char *);
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), agnsubg(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(Agraph_t *g, Agnode_t *n, int use_inedges, int use_outedges);
int agcountuniqedges(Agraph_t * g, Agnode_t * n, int in, int out);
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);
Agedge_t *agopp(Agedge_t *e);
int ageqedge(Agedge_t *e0, Agedge_t *e1);
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);
int agcopyattr(void *, void *);
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);
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
int *agpopdisc(Agraph_t *g);
void agpushdisc(Agraph_t *g, Agcbdisc_t *disc);
int agcallbacks(Agraph_t * g, int flag);
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 *);
char *agcanon(char *, int);
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);
ERROR REPORTING
typedef enum { AGWARN, AGERR, AGMAX, AGPREV } agerrlevel_t;
typedef int (*agusererrf) (char*);
agerrlevel_t agerrno;
agerrlevel_t agseterr(agerrlevel_t);
char *aglasterr(void);
int agerr(agerrlevel_t level, char *fmt, ...);
void agerrorf(char *fmt, ...);
void agwarningf(char *fmt, ...);
int agerrors(void);
agusererrf agseterrf(agusererrf);
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).
In the following, if a function has a parameter int createflag and the
object does not exist, the function will create the specified object if
createflag is non-zero; otherwise, it will return NULL.
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 integer 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.) The final argu‐
ment points to a discpline structure which can be used to tailor I/O,
memory allocation, and ID allocation. Typically, a NULL value will be
used to indicate the default discipline AgDefaultDisc. 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. agmemread
attempts to read a graph from the input string. agsetfile and agread‐
line are helper functions that simply set the current file name and
input line number for subsequent error reporting.
The functions agisdirected, agisundirected, agisstrict, and agissimple
can be used to query if a graph is directed, undirected, strict (at
most one edge with a given tail and head), or simple (strict with no
loops), respectively,
agsubg finds or creates a subgraph by name. agidsubg allows a program‐
mer to specify the subgraph by a unique integer ID. A new subgraph 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). The agparent function returns the immediate parent graph of
a subgraph, or itself if the graph is already a root graph.
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 agnsubg return the sizes of node, edge and sub‐
graph sets of a graph. The function agdegree returns the size of the
edge set of a nodes, and takes flags to select in-edges, out-edges, or
both. The function agcountuniqedges returns the size of the edge set
of a nodes, and takes flags to select in-edges, out-edges, or both.
Unlike agdegree, each loop is only counted once.
NODES
A node is created by giving a unique string name or programmer defined
integer 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. agidnode allows a programmer to specify the
node by a unique integer 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 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 or subgraph for an edge between the given
endpoints (with an optional multi-edge selector name) and returns it if
found or created. Note that, in undirected graphs, a search tries both
orderings of the tail and head nodes. If the name is NULL, then an
anonymous internal value is generated. agidedge allows a programmer to
create an edge by giving its unique integer ID. agsubedge performs a
similar operation on an existing edge and a subgraph. agfstin, agnx‐
tin, 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. agdeledge removes an edge from a graph or subgraph.
Note that an abstract edge has two distinct concrete representations:
as an in-edge and as an out-edge. In particular, the pointer as an out-
edge is different from the pointer as an in-edge. The function ageqedge
canonicalizes the pointers before doing a comparison and so can be used
to test edge equality. The sense of an edge can be flipped using agopp.
INTERNAL ATTRIBUTES
Programmer-defined values may be dynamically attached to graphs, sub‐
graphs, nodes, and edges. Such values are either character string data
(for I/O) or uninterpreted binary records (for implementing algorithms
efficiently).
STRING ATTRIBUTES
String attributes are handled automatically in reading and writing
graph files. A string attribute is identified by name and by an inter‐
nal symbol table entry (Agsym_t) created by Libcgraph. Attributes of
nodes, edges, and graphs (with their subgraphs) have separate names‐
paces. The contents of an Agsym_t have a char* name for the
attribute's name, a char* defval field for the attribute's default
value, and an int id field containing the index of the attribute's spe‐
cific value for an object in the object's array of attribute values.
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 exist‐
ing 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 NULL, the default is set for all graphs cre‐
ated 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 NULL is passed
as an argument it gets the first attribute; otherwise it returns the
next one in succession or returns NULL 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). Note that agset will fail unless the
attribute is first defined using agattr. agsafeset is a convenience
function that ensures the given attribute is declared before setting it
locally on an object.
It is sometimes convenient to copy all of the attributes from one
object to another. This can be done using agcopyattr. This fails and
returns non-zero of argument objects are different kinds, or if all of
the attributes of the source object have not been declared for the tar‐
get 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.
The cgraph parser handles HTML-like strings. These should be indistin‐
guishable 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.
agcanonStr returns a pointer to a version of the input string canoni‐
calized 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. For both of the functions, the input string must have been created
using agstrdup or agstrdup_html. Finally, agcanonStr is identical with
agcanonStr except it can be used with any character string. The second
argument indicates whether or not the string should be canonicalized as
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_t header;
/* programmer-defined fields follow */
} user_data_t;
Records are created and managed by Libcgraph. A programmer must explic‐
itly 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 of 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. The function aggetrec can also be used for lookup. agdelrec
deletes a named record from one object. 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
TRUE or FALSE. If move_to_front is TRUE, the record will be locked at
the head of the list, so it can be accessed directly by AGDATA(obj).
The lock can be subsequently released or reset by a call to aggetrec.
DISCIPLINES
(This section 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 NULL) 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 NULL is given for any of these
fields.
ID DISCIPLINE
An ID allocator discipline allows a client to control assignment of IDs
(uninterpreted integer values) to objects, and possibly how they are
mapped to and from strings.
struct Agiddisc_s { /* object ID allocator */
void *(*open) (Agraph_t * g, Agdisc_t*); /* associated with a graph */
long (*map) (void *state, int objtype, char *str, unsigned long *id, int createflag);
long (*alloc) (void *state, int objtype, unsigned long id);
void (*free) (void *state, int objtype, unsigned long id);
char *(*print) (void *state, int objtype, unsigned long id);
void (*close) (void *state);
};
open permits the ID discipline to initialize any data structures that
it maintains per individual graph. Its return value is then passed as
the first argument (void *state) 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 responsi‐
ble 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 integer 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 ta‐
ble, it can obtain them via new object callbacks.
IO DISCIPLINE
The I/O discipline provides an abstraction for the reading and writing
of graphs.
struct Agiodisc_s {
int (*fread)(void *chan, char *buf, int bufsize);
int (*putstr)(void *chan, char *str);
int (*flush)(void *chan); /* sync */
} ;
Normally, the FILE structure and its related functions are used for
I/O. At times, though, an application may need to use a totally differ‐
ent type of character source. The associated state or stream informa‐
tion is provided by the chan argument to agread or agwrite. The disci‐
pline function fread and putstr provide the corresponding functions for
read and writing.
MEMORY DISCIPLINE
Memory management in Libcgraph is handled on a per graph basis using
the memory discipline.
struct Agmemdisc_s { /* memory allocator */
void *(*open)(Agdisc_t*); /* 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);
} ;
The open function is used to initialize the memory subsystem, returning
state information that is passed to the calls to alloc, resize, and
free. The semantics of these should be comparable to the standard C
library functions malloc, realloc, and free, except that new space cre‐
ated by agalloc and agrealloc should be zeroed out. The close function
is used to terminate the memory subsystem, freeing any additional open
resources. For actual allocation, the library uses the functions agal‐
loc, agrealloc, and agfree, which provide simple wrappers for the
underlying discipline functions alloc, resize, and free.
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.
CALLBACKS
An Agcbdisc_t defines callbacks to be invoked by Libcgraph when ini‐
tializing, modifying, or finalizing graph objects. 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.
GENERIC OBJECTS
agroot takes any graph object (graph, subgraph, node, edge) and returns
the root graph in which it lives. agraphof does the same, except it is
the identity function on graphs and subgraphs. Note that there is no
function to return the least subgraph containing an object, in part
because this is not well-defined as nodes and edges may be in incompa‐
rable subgraphs.
agcontains(g,obj) returns non-zero if obj is a member of (sub)graph g.
agdelete(g,obj) is equivalent to agclose, agdelnode, and agdeledge for
obj being a graph, node or edge, respectively. It returns -1 if obj
does not belong to g.
AGDATA, AGID, and AGTYPE are macros returning the specified fields of
the argument object. The first is described in the RECORDS section
above. The second returns the unique integer ID associated with the
object. The last returns AGRAPH, AGNODE, and AGEDGE depending on the
type of the object.
agnameof returns a string descriptor for the object. It returns the
name of the node or graph, and the key of an edge. agobjkind is a syn‐
onym for AGTYPE.
ERROR REPORTING
The library provides a variety of mechanisms to control the reporting
of errors and warnings. At present, there are basically two types of
messages: warnings and errors. A message is only written if its type
has higher priority than a programmer-controlled minimum, which is
AGWARN by default. The programmer can set this value using agseterr,
which returns the previous value. Calling agseterr(AGMAX) turns off the
writing of messages.
The function agerr if the main entry point for reporting an anomaly.
The first argument indicates the type of message. Usually, the first
argument in AGWARN or AGERR to indicate warnings and errors, respec‐
tively. Sometimes additional context information is only available in
functions calling the function where the error is actually caught. In
this case, the calling function can indicate that it is continuing the
current error by using AGPREV as the first argument. The remaining
arguments to agerr are the same as the arguments to printf.
The functions agwarningf and agerrorf are shorthand for
agerr(AGERR,...) and agerr(AGWARN,...), respectively.
Some applications desire to directly control the writing of messages.
Such an application can use the function agseterrf to register the
function that the library should call to actually write the message.
The previous error function is returned. By default, the message is
written to stderr.
Errors not written are stored in a log file. The last recorded error
can be retreived by calling aglasterr.
The function agerrors returns non-zero if errors have been reported.
EXAMPLE PROGRAM
#include <cgraph.h>
typedef struct {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 ALSOLibcdt(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 differ‐
ent 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.
The library is not thread safe.
AUTHOR
Stephen North, north@research.att.com, AT&T Research.
28 FEBRUARY 2013 LIBCGRAPH(3)
