curl/docs/libcurl/libcurl.3

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.TH libcurl 5 "14 August 2001" "libcurl 7.8.1" "libcurl overview"
.SH NAME
libcurl \- client-side URL transfers
.SH 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.

libcurl can also be used directly from within your Java, PHP, Perl, Ruby or
Tcl programs as well, look elsewhere for documentation on this!

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

When using libcurl you init your session and get a handle, which you use as
input to the following interface functions you use. Use \fIcurl_easy_init()\fP
to get the handle.

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.  \fIcurl_easy_setopt()\fP is there for this.

When all is setup, you tell libcurl to perform the transfer using
\fIcurl_easy_perform()\fP.  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
\fIcurl_easy_cleanup()\fP.  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 Connections.

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

.RS
.TP 10
.B curl_version()
displays the libcurl version
.TP
.B curl_getdate()
converts a date string to time_t
.TP
.B curl_getenv()
portable environment variable reader
.TP
.B curl_easy_getinfo()
get information about a performed transfer
.TP
.B curl_formadd()
helps building a HTTP form POST
.TP
.B curl_formfree()
free a list built with curl_formparse()/curl_formadd()
.TP
.B curl_slist_append()
builds a linked list
.TP
.B curl_slist_free_all()
frees a whole curl_slist
.TP
.B curl_mprintf()
portable printf() functions
.TP
.B curl_strequal()
portable case insensitive string comparisons
.RE

.SH "LINKING WITH LIBCURL"
Starting with 7.7.2 (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.
.SH "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!
.SH "PORTABILITY"
libcurl works
.B exactly
the same, on any of the platforms it compiles and builds on.

There's only one caution, and that is the win32 platform that may(*) require
you to init the winsock stuff before you use the libcurl functions. Details on
this are noted on the curl_easy_init() man page.

(*) = it appears as if users of the cygwin environment get this done
automatically, also libcurl 7.8.1 and later can handle this for you.
.SH "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.
.SH "PERSISTANT CONNECTIONS"
With libcurl 7.7, persistant connections were added. Persistant connections
means that libcurl can re-use the same connection for several transfers, if
the conditions are right.

libcurl will *always* attempt to use persistant 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 persistant 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
.SH "COMPATIBILITY WITH OLDER LIBCURLS"
Repeated curl_easy_perform() calls on the same handle were not supported in
pre-7.7 versions, and caused confusion and undefined behaviour.