libcurl basics

The engine in the curl command-line tool is libcurl. libcurl is also the
engine in thousands of tools, services and applications out there today,
performing their Internet data transfers.

C API

libcurl is a library of functions that are provided with a C API, for
applications written in C. You can easily use it from C++ too, with only a few
considerations (see libcurl for C++ programmers. For
other languages, there exist “bindings” that work as intermediate layers
between libcurl the library and corresponding functions for the particular
language you like.

Transfer oriented

We have designed libcurl to be transfer oriented usually without forcing users
to be protocol experts or in fact know much at all about networking or the
protocols involved. You setup a transfer with as many details and specific
information as you can and want, and then you tell libcurl to perform that
transfer.

That said, networking and protocols are areas with lots of pitfalls and
special cases so the more you know about these things, the more you will be
able to understand about libcurl’s options and ways of working. Not to
mention, such knowledge is invaluable when you are debugging and need to
understand what to do next when things don’t go as you intended.

The most basic libcurl using application can be as small as just a couple of
lines of code, but most applications will, of course, need more code than that.

Simple by default, more on demand

libcurl generally does the simple and basic transfer by default, and if you
want to add more advanced features, you add that by setting the correct
options. For example, libcurl doesn’t support HTTP cookies by default but it
does once you tell it.

This makes libcurl’s behaviors easier to guess and depend on, and also it makes
it easier to maintain old behavior and add new features. Only applications
that actually ask for and use the new features will get that behavior.