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       librrd - RRD library functions


       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.


       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.


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

       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))

       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))

       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

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

               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.


       RRD Contributors <>