-iquotedir

[ali hagigat]

This option does not make sense! When we use -I option, it is not used
for ‘#include <file >’. Is that right? (If true, -I is equal to
-iquotedir)
Or -I search path is used for ‘#include <file >’ but the file is
tagged as a system file?

My another concern is the explanation of -I option!!:
"If a standard system include directory, or a directory specified with
‘-isystem’, is also specified with ‘-I’, the ‘-I’ option will be
ignored."

In this case -I option and the directory after that are not ignored!!
-I is replaced with -isystem. When you have written "ignored", it
suggests that -I does not be considered.

Then the manual continues:
"The directory will still be searched but as a system directory at its
normal position in the system
include chain"

When a beginner reads your sentence he asks what is the system include
chain? and what is the normal position? Is it the point where -I has
been used on the command line? or it is pointing to the directory of
the system which is used by gcc when searching headers.