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           This  is  a  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 thirty custom bindings available that bring libcurl
           access to your favourite language. Look elsewhere for documentation  on
           libcurl  has  a  global  constant  environment that you must set up and
           maintain  while  using  libcurl.   This  essentially  means  you   call
           curl_global_init(3)    at    the    start    of    your   program   and
           curl_global_cleanup(3) at the end.   See  GLOBAL  CONSTANTS  below  for
           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  returns  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 details 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
                         gets  detailed libcurl (and other used libraries) version
                         converts a date string to time_t
                         get information about a performed transfer
           installed  with  the rest of the curl stuff when 'make install' is per-
           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.


           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!


           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.
           The global environment functions are not thread-safe.  See GLOBAL  CON-
           STANTS below for details.


           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.
           cate  resources (e.g. the memory for the GNU TLS tree mentioned above),
           so the companion function curl_global_cleanup() releases them.
           The basic rule for constructing a program that uses  libcurl  is  this:
           Call  curl_global_init(),  with a CURL_GLOBAL_ALL argument, immediately
           after the program starts, while it is still only one thread and  before
           it  uses libcurl at all.  Call curl_global_cleanup() immediately before
           the program exits, when the program is again only one thread and  after
           its last use of libcurl.
           You  can  call  both of these multiple times, as long as all calls meet
           these requirements and the number of calls to each is the same.
           It isn't actually required that the functions be called at  the  begin-
           ning  and  end of the program -- that's just usually the easiest way to
           do it.  It is required that the  functions  be  called  when  no  other
           thread in the program is running.
           These  global  constant  functions are not thread safe, so you must not
           call them when any other thread in the program is  running.   It  isn't
           good  enough that no other thread is using libcurl at the time, because
           these functions internally call similar functions of  other  libraries,
           and  those  functions are similarly thread-unsafe.  You can't generally
           know what these libraries are, or whether other threads are using them.
           The  global  constant  situation  merits special consideration when the
           code you are writing to use libcurl is not the main program, but rather
           a  modular piece of a program, e.g. another library.  As a module, your
           code doesn't know about other parts of the program -- it  doesn't  know
           whether  they use libcurl or not.  And its code doesn't necessarily run
           at the start and end of the whole program.
           A module like this must have global constant functions of its own, just
           like curl_global_init() and curl_global_cleanup().  The module thus has
           control at the beginning and end of the program and has a place to call
           the  libcurl  functions.   Note that if multiple modules in the program
           use libcurl, they all will separately call the libcurl  functions,  and
           that's  OK  because  only  the  first  curl_global_init()  and the last
           curl_global_cleanup() in a program change anything.   (libcurl  uses  a
           reference count in static memory).
           In  a  C++ module, it is common to deal with the global constant situa-
           tion by defining a special class that represents  the  global  constant
           environment  of the module.  A program always has exactly one object of
           the class, in static storage.   That  way,  the  program  automatically
           calls  the  constructor  of the object as the program starts up and the
           destructor as it terminates.  As the author of this libcurl-using  mod-
           ule,  you  can  make  the  constructor  call curl_global_init() and the
           destructor call curl_global_cleanup() and  satisfy  libcurl's  require-
           ments without your user having to think about it.
           curl_global_init()  has an argument that tells what particular parts of
           at all: curl_easy_init() sets up the environment itself  if  it  hasn't
           been  done yet.  The resources it acquires to do so get released by the
           operating system automatically when the program exits.
           This failsafe feature exists mainly for backward compatibility  because
           there was a time when the global functions didn't exist.  Because it is
           sufficient only in the simplest of programs, it is not recommended  for
           any program to rely on it.

    libcurl 7.9.6 19 March 2002 libcurl(3)


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