LIBGVPR(3)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 pro‐
vides 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 ele‐
ments 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 func‐
tion 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 ALSOgvpr(1), awk(1), cgraph(3)AUTHORS
Emden Gansner (erg@research.att.com).
15 OCTOBER 2013 LIBGVPR(3)
