libcurl(3)

NAME

       libcurl - client-side URL transfers

DESCRIPTION

       This  is  an  short  overview on how to use libcurl in your C programs.
       There are specific man pages for each function mentioned in here. There
       are  also  the libcurl-easy(3) man page, the libcurl-multi(3) man page,
       the libcurl-share(3) man page and the libcurl-tutorial(3) man page  for
       in-depth understanding on how to program with libcurl.

       There  are  more  than  a  twenty  custom bindings available that bring
       libcurl access to your favourite language. Look elsewhere for  documen-
       tation on those.

       All  applications  that  use  libcurl  should  call curl_global_init(3)
       exactly once before any libcurl function can be used. After  all  usage
       of libcurl is complete, it must call curl_global_cleanup(3). In between
       those two calls, you can use libcurl as described below.

       To  transfer  files,  you  always  set  up  an  "easy   handle"   using
       curl_easy_init(3),  but  when you want the file(s) transferred you have
       the option of using the "easy" interface, or the "multi" interface.

       The easy interface is a  synchronous  interface  with  which  you  call
       curl_easy_perform(3)  and  let it perform the transfer. When it is com-
       pleted, the function return and you  can  continue.  More  details  are
       found in the libcurl-easy(3) man page.

       The  multi  interface  on  the other hand is an asynchronous interface,
       that you call and that performs only a little piece of the transfer  on
       each  invoke. It is perfect if you want to do things while the transfer
       is in progress, or similar. The multi interface allows you to  select()
       on  libcurl action, and even to easily download multiple files simulta-
       neously using a single thread.  See  further  deails  in  the  libcurl-
       multi(3) man page.

       You can have multiple easy handles share certain data, even if they are
       used in different threads. This magic is setup using the  share  inter-
       face, as described in the libcurl-share(3) man page.

       There  is  also  a  series of other helpful functions to use, including
       these:

              curl_version_info()
                     gets detailed libcurl (and other used libraries)  version
                     info

              curl_getdate()
                     converts a date string to time_t

              curl_easy_getinfo()
                     get information about a performed transfer

              curl_formadd()
                     helps building an HTTP form POST

              curl_formfree()
                     free a list built with curl_formadd(3)

              curl_slist_append()
                     builds a linked list

              curl_slist_free_all()
                     frees a whole curl_slist

LINKING WITH LIBCURL

       On  unix-like  machines,  there's  a  tool  named curl-config that gets
       installed with the rest of the curl stuff when 'make install'  is  per-
       formed.

       curl-config  is  added  to make it easier for applications to link with
       libcurl and developers to learn about libcurl and how to use it.

       Run 'curl-config --libs' to get the  (additional)  linker  options  you
       need  to  link with the particular version of libcurl you've installed.
       See the curl-config(1) man page for further details.

       Unix-like operating system that ship libcurl as part of their distribu-
       tions  often don't provide the curl-config tool, but simply install the
       library and headers in the common path for this purpose.

LIBCURL SYMBOL NAMES

       All public functions in the libcurl interface are prefixed with 'curl_'
       (with  a  lowercase  c).  You  can  find other functions in the library
       source code, but other prefixes indicate that the functions are private
       and may change without further notice in the next release.

       Only use documented functions and functionality!

PORTABILITY

       libcurl works exactly the same, on any of the platforms it compiles and
       builds on.

THREADS

       Never ever call curl-functions simultaneously  using  the  same  handle
       from  several  threads.  libcurl  is thread-safe and can be used in any
       number of threads, but you must use separate curl handles if  you  want
       to use libcurl in more than one thread simultaneously.

PERSISTENT CONNECTIONS

       Persistent  connections  means that libcurl can re-use the same connec-
       tion for several transfers, if the conditions are right.

       libcurl will always attempt to use persistent connections. Whenever you
       use curl_easy_perform(3) or curl_multi_perform(3), libcurl will attempt
       to use an existing connection to do the transfer, and  if  none  exists
       it'll open a new one that will be subject for re-use on a possible fol-
       lowing call to curl_easy_perform(3) or curl_multi_perform(3).

       To allow libcurl to take full advantage of persistent connections,  you
       should  do  as  many  of your file transfers as possible using the same
       curl handle. When you call curl_easy_cleanup(3), all the possibly  open
       connections held by libcurl will be closed and forgotten.

       Note  that  the options set with curl_easy_setopt(3) will be used in on
       every repeated curl_easy_perform(3) call.

libcurl 7.9.6                    19 March 2002                      libcurl(3)