libcurl - client-side URL transfers


       This  is  an overview on how to use libcurl in your C pro-
       grams. There are specific man pages for each function men-
       tioned  in  here. There's also the libcurl-the-guide docu-
       ment 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 doc-
       umentation on those.

       All    applications   that   use   libcurl   should   call
       curl_global_init() exactly once before any  libcurl  func-
       tion  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 ses-
       sion 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  transfer,  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  trans-
       fer 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 per-
       sistant 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-

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

                        displays the libcurl version

                        converts a date string to time_t

                        portable environment variable reader

                        get information about a performed  trans-

                        helps building a HTTP form POST

                        free   a   list   built  with  curl_form-

                        builds a linked list

                        frees a whole curl_slist

                        portable printf() functions

                        portable case insensitive string  compar-


       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 performed.

       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.


       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.

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


       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 means that libcurl can  re-use  the
       same  connection  for several transfers, if the conditions
       are right.

       libcurl will *always* attempt to  use  persistent  connec-
       tions.  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 sub-
       ject  for  re-use  on  a  possible   following   call   to

       To allow libcurl to take full advantage of persistent con-
       nections, 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

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