GCC for beginners

Header file naming

On Unix, there's a given hierarchy of header files. So when you install the C library header files (equivalent to UnixLib) they go in /usr/include. So you get files like:

/usr/include/stdio.h
/usr/include/string.h
/usr/include/setjmp.h
/usr/include/time.h
/usr/include/sys/time.h
/usr/include/sys/quota.h
/usr/include/net/ethernet.h

When you install other packages they slot into this structure. For example the GPIB driver library I've been using today lives in:

/usr/include/gpib/ib.h

and if you install the Linux kernel headers you get things like:

/usr/include/linux/adfs_fs.h (the ADFS driver for Linux)
/usr/include/linux/joystick.h

and so on.

The name inside the pointy brackets <> is effectively the path without /usr/include on the front. So

#include <sys/types.h>

refers to

/usr/include/sys/types.h

while

#include <bits/types.h>

refers to

/usr/include/bits/types.h

They're different files, and they have different pathnames (in fact, in glibc on Linux, sys/types.h has a #include <bits/types.h>). In the list above notice there are two time.h files - you'd refer to the first one as plain <time.h> and the second as <sys/time.h>

Of course it's slightly more complicated than that - /usr/include is a system-wide path so you need to be the machine administrator to add things to it. If I'm not administrator I might put some header files in some other directory (/home/theo/myincludes say) and use a -isystem to refer to them.