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librrd(3)			    rrdtool			     librrd(3)

NAME
       librrd - RRD library functions

DESCRIPTION
       librrd contains most of the functionality in RRDTool.  The command line
       utilities and language bindings are often just wrappers around the code
       contained in librrd.

       This manual page documents the librrd API.

       NOTE: This document is a work in progress, and should be considered
       incomplete as long as this warning persists.  For more information
       about the librrd functions, always consult the source code.

CORE FUNCTIONS
       rrd_dump_cb_r(char *filename, int opt_header, rrd_output_callback_t cb,
       void *user)
	   In some situations it is necessary to get the output of "rrd_dump"
	   without writing it to a file or the standard output. In such cases
	   an application can ask rrd_dump_cb_r to call an user-defined
	   function each time there is output to be stored somewhere. This can
	   be used, to e.g. directly feed an XML parser with the dumped output
	   or transfer the resulting string in memory.

	   The arguments for rrd_dump_cb_r are the same as for rrd_dump_opt_r
	   except that the output filename parameter is replaced by the user-
	   defined callback function and an additional parameter for the
	   callback function that is passed untouched, i.e. to store
	   information about the callback state needed for the user-defined
	   callback to function properly.

	   Recent versions of rrd_dump_opt_r internally use this callback
	   mechanism to write their output to the file provided by the user.

	       size_t rrd_dump_opt_cb_fileout(
		   const void *data,
		   size_t len,
		   void *user)
	       {
		   return fwrite(data, 1, len, (FILE *)user);
	       }

	   The associated call for rrd_dump_cb_r looks like

	       res = rrd_dump_cb_r(filename, opt_header,
		   rrd_dump_opt_cb_fileout, (void *)out_file);

	   where the last parameter specifies the file handle
	   rrd_dump_opt_cb_fileout should write to. There's no specific
	   condition for the callback to detect when it is called for the
	   first time, nor for the last time. If you require this for
	   initialization and cleanup you should do those tasks before and
	   after calling rrd_dump_cr_r respectively.

UTILITY FUNCTIONS
       rrd_random()
	   Generates random numbers just like random().	 This further ensures
	   that the random number generator is seeded exactly once per
	   process.

       rrd_add_ptr(void ***dest, size_t *dest_size, void *src)
	   Dynamically resize the array pointed to by "dest".  "dest_size" is
	   a pointer to the current size of "dest".  Upon successful
	   realloc(), the "dest_size" is incremented by 1 and the "src"
	   pointer is stored at the end of the new "dest".  Returns 1 on
	   success, 0 on failure.

	       type **arr = NULL;
	       type *elem = "whatever";
	       size_t arr_size = 0;
	       if (!rrd_add_ptr(&arr, &arr_size, elem))
		   handle_failure();

       rrd_add_strdup(char ***dest, size_t *dest_size, char *src)
	   Like "rrd_add_ptr", except adds a "strdup" of the source string.

	       char **arr = NULL;
	       size_t arr_size = NULL;
	       char *str  = "example text";
	       if (!rrd_add_strdup(&arr, &arr_size, str))
		   handle_failure();

       rrd_free_ptrs(void ***src, size_t *cnt)
	   Free an array of pointers allocated by "rrd_add_ptr" or
	   "rrd_add_strdup".  Also frees the array pointer itself.  On return,
	   the source pointer will be NULL and the count will be zero.

	       /* created as above */
	       rrd_free_ptrs(&arr, &arr_size);
	       /* here, arr == NULL && arr_size == 0 */

       rrd_mkdir_p(const char *pathname, mode_t mode)
	   Create the directory named "pathname" including all of its parent
	   directories (similar to "mkdir -p" on the command line - see
	   mkdir(1) for more information). The argument "mode" specifies the
	   permissions to use. It is modified by the process's "umask". See
	   mkdir(2) for more details.

	   The function returns 0 on success, a negative value else. In case
	   of an error, "errno" is set accordingly. Aside from the errors
	   documented in mkdir(2), the function may fail with the following
	   errors:

	   EINVAL
	       "pathname" is "NULL" or the empty string.

	   ENOMEM
	       Insufficient memory was available.

	   any error returned by stat(2)

	   In contrast to mkdir(2), the function does not fail if "pathname"
	   already exists and is a directory.

AUTHOR
       RRD Contributors <rrd-developers@lists.oetiker.ch>

1.4.8				  2013-05-23			     librrd(3)
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