API

libcurl exposes its public surface via headers in include/curl/. Application code only ever includes <curl/curl.h>; that header pulls in the rest. The API is divided into a handful of independent surfaces.

Surface	Header	Wiki page
Easy interface	curl/easy.h, curl/curl.h	Easy
Multi interface	curl/multi.h	Multi
URL API	curl/urlapi.h	URL
Header API	curl/header.h	covered in Easy
WebSockets	curl/websockets.h	covered in WebSockets
Share	curl/curl.h	covered in Multi
Programmatic options/info	curl/options.h	covered in Easy

ABI: SONAME 4 since 2006. New options are additive only. The version macros (LIBCURL_VERSION_MAJOR/MINOR/PATCH, LIBCURL_VERSION_NUM) live in include/curl/curlver.h.

The exhaustive per-option documentation lives under docs/libcurl/ (one curldown file per CURLOPT_*, CURLINFO_*, CURLMOPT_*, CURLSHOPT_*). The pages here describe how the surfaces fit together and the most common usage patterns.