HelenOS sources

common/include/ctype.h
kernel/generic/common/include/ctype.h
uspace/lib/c/common/include/ctype.h
uspace/lib/http/include/http/ctype.h
uspace/lib/posix/include/common/ctype.h
uspace/lib/posix/include/posix/ctype.h
uspace/lib/uri/internal/ctype.h
HelenOS homepage, sources at GitHub