https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110226
Bug ID: 110226 Summary: GCC ignores include of non-existent header Product: gcc Version: 13.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: jpegqs at gmail dot com Target Milestone: --- Try compiling this code with g++: #if __has_include("quadmath123.h") #endif #include <quadmath123.h> You shouldn't have "quadmath123.h", but GCC will compile this without error. Reproduced in every version of GCC since __has_include was supported (GCC 4.9.2). Occurs in Boost headers when <quadmath.h> is not installed.