curl / Development / Internals

curl internals

The canonical libcurl internals documentation is now in the everything curl book. This file lists supported versions of libs, tools and operating systems.


We write curl and libcurl to compile with C89 compilers. On 32-bit and up machines. Most of libcurl assumes more or less POSIX compliance but that is not a requirement.

We write libcurl to build and work with lots of third party tools, and we want it to remain functional and buildable with these and later versions (older versions may still work but is not what we work hard to maintain):


We aim to support these or later versions.

Operating Systems

On systems where configure runs, we aim at working on them all - if they have a suitable C compiler. On systems that do not run configure, we strive to keep curl running correctly on:

Build tools

When writing code (mostly for generating stuff included in release tarballs) we use a few "build tools" and we make sure that we remain functional with these versions:

Library Symbols

All symbols used internally in libcurl must use a Curl_ prefix if they are used in more than a single file. Single-file symbols must be made static. Public ("exported") symbols must use a curl_ prefix. (There are exceptions, but they are to be changed to follow this pattern in future versions.) Public API functions are marked with CURL_EXTERN in the public header files so that all others can be hidden on platforms where this is possible.