curl/docs/libcurl/libcurl.3

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.TH libcurl 3 "19 March 2002" "libcurl 7.9.6" "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 are also the
\fIlibcurl-easy(3)\fP man page, the \fIlibcurl-multi(3)\fP man page, the
\fIlibcurl-share(3)\fP man page and the \fIlibcurl-the-guide\fP document for
further reading on how to do programming with libcurl.

There exist more than 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 \fIcurl_global_init(3)\fP
exactly once before any libcurl function can be used. After all usage of
libcurl is complete, it \fBmust\fP call \fIcurl_global_cleanup(3)\fP. In
between those two calls, you can use libcurl as described below.

To transfer files, you always set up an "easy handle" using
\fIcurl_easy_init(3)\fP, 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
\fIcurl_easy_perform(3)\fP and let it perform the transfer. When it is
completed, the function return and you can continue. More details are found in
the \fIlibcurl-easy(3)\fP 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 simultaneously using a single thread. See further deails in the \fIlibcurl-multi(3)\fP 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 interface, as
described in the \fIlibcurl-share(3)\fP man page.

There is also a series of other helpful functions to use, including these:
.RS
.IP curl_version_info()
gets detailed libcurl (and other used libraries) version info
.IP curl_getdate()
converts a date string to time_t
.IP curl_easy_getinfo()
get information about a performed transfer
.IP curl_formadd()
helps building an HTTP form POST
.IP curl_formfree()
free a list built with \fIcurl_formadd(3)\fP
.IP curl_slist_append()
builds a linked list
.IP curl_slist_free_all()
frees a whole curl_slist
.RE

.SH "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 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. See the
\fIcurl-config(1)\fP man page for further details.

Unix-like operating system that ship libcurl as part of their distributions
often don't provide the curl-config tool, but simply install the library and
headers in the common path for this purpose.

.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 that 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.
.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 "PERSISTENT CONNECTIONS"
Persistent connections means that libcurl can re-use the same connection for
several transfers, if the conditions are right.

libcurl will \fBalways\fP attempt to use persistent connections. Whenever you
use \fIcurl_easy_perform(3)\fP or \fIcurl_multi_perform(3)\fP, 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 \fIcurl_easy_perform(3)\fP or \fIcurl_multi_perform(3)\fP.

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 \fIcurl_easy_cleanup(3)\fP, all the possibly open connections held by
libcurl will be closed and forgotten.

Note that the options set with \fIcurl_easy_setopt(3)\fP will be used in on
every repeated \fIcurl_easy_perform(3)\fP call.