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>

1.4.7                                              2009-11-15                                          librrd(3)