LIBGVPR(3) Library Functions Manual LIBGVPR(3)

# [NAME](#NAME)

**libgvpr** - library for graph filtering

# [SYNOPSIS](#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](#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)](/man/os/graphviz/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 *opts-&gt;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-&gt;flags*, the output graphs will be stored in an array pointed to be *opts-&gt;outgraphs* and the count will be stored in *opts-&gt;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](#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-&gt;err* function will have been called. If, however, *GV\_USE\_EXIT* is set in *opts-&gt;flags*, **gvpr** will call [exit(3)](/man/os/graphviz/exit.3) in case of an error.

# [SEE ALSO](#SEE_ALSO)

[**gvpr**(1)](/man/os/graphviz/gvpr.1), [**awk**(1)](/man/os/graphviz/awk.1), [**cgraph**(3)](/man/os/graphviz/cgraph.3)

# [AUTHORS](#AUTHORS)

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

15 OCTOBER 2013

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Document: gvpr(3) from graphviz 15.1.1-r1 (Chainguard OS)
Source: https://gitlab.com/graphviz/graphviz