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95 lines
4.0 KiB
Plaintext
95 lines
4.0 KiB
Plaintext
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How To Use Libcurl In Your C/C++ Program
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[ libcurl can be used directly from within your PHP or Perl programs as well,
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look elsewhere for documentation on this ]
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The interface is meant to be very simple for applictions/programmers, hence
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the name "easy". We have therefore minimized the number of entries.
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The Easy Interface
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When using the easy interface, you init your session and get a handle, which
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you use as input to the following interface functions you use. Use
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curl_easy_init() to get the handle.
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You continue by setting all the options you want in the upcoming transfer,
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most important among them is the URL itself (you can't transfer anything
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without a specified URL as you may have figured out yourself). You might want
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to set some callbacks as well that will be called from the library when data
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is available etc. curl_easy_setopt() is there for this.
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When all is setup, you tell libcurl to perform the transfer using
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curl_easy_perform(). It will then do the entire operation and won't return
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until it is done or failed.
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After the transfer has been made, you cleanup the session with
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curl_easy_cleanup() and libcurl is entirely off the hook! If you want
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persistant connections, you don't cleanup immediately, but instead run ahead
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and perform other transfers. See the chapter below for Persistant
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Connections.
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While the above mentioned four functions are the main functions to use in the
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easy interface, there is a series of other helpful functions to use. They
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are:
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curl_version() - displays the libcurl version
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curl_getdate() - converts a date string to time_t
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curl_getenv() - portable environment variable reader
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curl_easy_getinfo() - get information about a performed transfer
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curl_formparse() - helps building a HTTP form POST
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curl_formfree() - free a list built with curl_formparse()
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curl_slist_append() - builds a linked list
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curl_slist_free_all() - frees a whole curl_slist
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For details on these, read the separate man pages.
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Portability
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libcurl works *exactly* the same, on any of the platforms it compiles and
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builds on.
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There's only one caution, and that is the win32 platform that may(*) require
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you to init the winsock stuff before you use the libcurl functions. Details
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on this are noted on the curl_easy_init() man page.
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(*) = it appears as if users of the cygwin environment get this done
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automatically.
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Threads
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Never *ever* call curl-functions simultaneously using the same handle from
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several threads. libcurl is thread-safe and can be used in any number of
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threads, but you must use separate curl handles if you want to use libcurl in
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more than one thread simultaneously.
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Persistant Connections
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With libcurl 7.7, persistant connections were added. Persistant connections
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means that libcurl can re-use the same connection for several transfers, if
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the conditions are right.
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libcurl will *always* attempt to use persistant connections. Whenever you use
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curl_easy_perform(), libcurl will attempt to use an existing connection to do
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the transfer, and if none exists it'll open a new one that will be subject
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for re-use on a possible following call to curl_easy_perform().
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To allow libcurl to take full advantage of persistant connections, you should
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do as many of your file transfers as possible using the same curl
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handle. When you call curl_easy_cleanup(), all the possibly open connections
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held by libcurl will be closed and forgotten.
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Note that the options set with curl_easy_setopt() will be used in on every
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repeat curl_easy_perform() call
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Compatibility with older libcurls
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Repeated curl_easy_perform() calls on the same handle were not supported in
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pre-7.7 versions, and caused confusion and defined behaviour.
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