Question

when we use #include < stdio.h > in linux platform, the compiler will search the stdio.h in /usr/include. How to change the path of using #include<>?
thank you.

I asked the question because of this : when I use the C standard function isdigit(), if “#include< ctype.h >” is not added, the program generates a warning but no error. But if “#include < ctype.h >” is added,it will generate an error when linking.(My compiler is not the standard gcc.)

I wonder why?

Answer 1

 -I dir
     Add the directory dir to the list of directories to be
     searched for header files.  Directories named by -I are
     searched before the standard system include directories.