libcurl

libcurl(3)                     libcurl overview                     libcurl(3)



NAME
       libcurl - client-side URL transfers

DESCRIPTION
       This is an overview on how to use libcurl in your C programs. There are
       specific man pages for each function mentioned in  here.  There's  also
       the  libcurl-the-guide  document for a complete tutorial to programming
       with libcurl.

       There are a dozen custom bindings that bring  libcurl  access  to  your
       favourite language. Look elsewhere for documentation on those.

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

       When using libcurl's "easy" interface you init your session and  get  a
       handle, which you use as input to the easy interface functions you use.
       Use curl_easy_init() to get the handle. There is  also  the  so  called
       "multi" interface, try the libcurl-multi(3) man page for an overview of
       that.

       You continue by setting all the options you want in the upcoming trans-
       fer,  most  important  among them is the URL itself (you can't transfer
       anything without a specified URL as you may have figured out yourself).
       You  might  want to set some callbacks as well that will be called from
       the library when data is available etc.   curl_easy_setopt()  is  there
       for this.

       When  all  is  setup,  you  tell  libcurl to perform the transfer using
       curl_easy_perform().  It will then do the entire  operation  and  won't
       return until it is done (successfully or not).

       After  the  transfer  has  been  made, you can set new options and make
       another transfer, or if you're done, cleanup  the  session  by  calling
       curl_easy_cleanup().   If  you  want  persistant connections, you don't
       cleanup immediately, but instead run ahead and perform other  transfers
       using  the  same  handle.  See the chapter below for Persistant Connec-
       tions.

       There is also a series of other helpful functions to use. They are:


              curl_version()
                        displays the libcurl version

              curl_getdate()
                        converts a date string to time_t

              curl_getenv()
                        portable environment variable reader

              curl_easy_getinfo()
                        get information about a performed transfer

              curl_formadd()
                        helps building a HTTP form POST

              curl_formfree()
                        free a list built with curl_formparse()/curl_formadd()

              curl_slist_append()
                        builds a linked list

              curl_slist_free_all()
                        frees a whole curl_slist

              curl_mprintf()
                        portable printf() functions

              curl_strequal()
                        portable case insensitive string comparisons


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.

       For details, see the curl-config.1 man page.

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 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.

PERSISTANT 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(), 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  following  call  to
       curl_easy_perform().

       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(), all the possibly open
       connections held by libcurl will be closed and forgotten.

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



libcurl 7.9.6                    19 March 2002                      libcurl(3)