ISYSROOTusrinclude

ISYSROOTusrinclude refers to the usr/include directory inside a system root (sysroot) used by compilers and build tools. The sysroot is a directory that serves as the root filesystem for a target system during compilation, allowing developers to build for another architecture or platform without relying on headers and libraries from the host system. In this context, ISYSROOT represents the path to that sysroot, and the path ISYSROOT/usr/include contains the standard system header files for the target environment.

The concept of a sysroot is central to cross-compilation and SDK production. A compiler can be instructed to treat a specified directory as the root of the target filesystem, using options such as -isysroot. By directing include searches to ISYSROOT/usr/include, the compiler uses the target’s header files (for example, libc, libc++ or other system headers) rather than the host’s equivalents. This helps ensure compatibility with the target’s ABI and libraries.

In practice, a build may reference ISYSROOT/usr/include directly or rely on the -isysroot flag to set the sysroot, with additional -I options to add other include paths. Tools such as clang, gcc, and build systems like CMake or autotools commonly use these settings when producing software for different platforms or architectures, including embedded systems or macOS/iOS SDKs. Misconfiguration can lead to missing headers or mismatched libraries, so accurate sysroot setup is important.

See also: sysroot, -isysroot, SDK, cross-compilation.