LIBGVPR(3) Introduction to Library Functions LIBGVPR(3)

NAME

libgvpr - library for graph filtering

SYNOPSIS

#include <graphviz/gvpr.h>


/* If set, gvpr calls exit() on errors */
#define GV_USE_EXIT 1
/* If set, gvpr stores output graphs in gvpropts */
#define GV_USE_OUTGRAPH 2

typedef ssize_t (*gvprwr) (void*, const char *buf, size_t nbyte, void*);

typedef struct {
Agraph_t** ingraphs; /* NULL-terminated array of input graphs */
int n_outgraphs; /* if GV_USE_OUTGRAPH set, output graphs */
Agraph_t** outgraphs;
gvprwr out; /* write function for stdout */
gvprwr err; /* write function for stderr */
int flags;
} gvpropts;

extern int gvpr (int argc, char *argv[], gvpropts* opts);

DESCRIPTION

The gvpr library allows an application to perform general-purpose
graph manipulation and filtering based on an awk-like language. (For
a more complete description of this language, see gvpr(1).)

The library has a single entry point: the gvpr() function. This
provides a standard argc/argv interface, along with a structure to
support in-core graphs, application print functions, along with
additional options.

When called, gvpr() processes any flags provided in the argv array,
and compiles the gvpr program to be run (provided either via the -f
flag or as an item in argv). It then runs the program on each input
graph. If opt->ingraphs is non-NULL, this is taken as a NULL-
terminated array of in-core graphs to be used as input. Otherwise,
the unprocessed elements of argv are taken to be the names of files
containing graphs to be processed. (If none remain, gvpr will read
from stdin.)

Normally, gvpr writes any output graph to stdout. However, if the
flag GV_USE_OUTGRAPH is set in opts->flags, the output graphs will be
stored in an array pointed to be opts->outgraphs and the count will
be stored in opts->n_outgraphs. In this case, the application must
call agclose() on each output graph when it is done with it.

The application can override the default write functions for stdout
and stderr using the out and err fields in opts. When called by gvpr,
the second argument will point to a buffer of characters to be
written, while the third argument provides the number of characters.
The function should return the number of bytes actually written.

RETURN VALUES

Normally, gvpr returns 0 on success and non-zero if an error occurs.
Any relevant error message will have been written to stderr or the
application's opts->err function will have been called. If, however,
GV_USE_EXIT is set in opts->flags, gvpr will call exit(3) in case of
an error.

SEE ALSO

gvpr(1), awk(1), cgraph(3)

AUTHORS

Emden Gansner (erg@research.att.com).


15 OCTOBER 2013 LIBGVPR(3)