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>