I just downloaded some new header files and have a folder of them that I wish to make available. First, I would like to make them available to any file wishing to use them. So, I would like to be able to include the new header file (call it newheader.h) where I want, just like math.h, for example. Where should I put it?

Second, I wish to make these files available to all users. I have root permissions. Is there a special directory I need to put it in? Thanks so much!

Store them in /usr/local/include. From http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/usr.html, items in this directory are "... safe from being overwritten when the system software is updated", which is important since you do not want the headers files you have downloaded to get clobbered by system updates, which might happen if you put them in /usr/include.

On MY system, the /usr/local/include/ directory exists, and is empty. The Filsystem Hierarchy Standard says (FHS 3.0) the directory to use is /usr/local/include. Files should be world-readable (0444) and directories should be searchable (0555).

The question is, what do you want to achieve?

Usually you have three scenarios:

• development


• local installation (in your $HOME)


• global installation

For the first 2, you should probably use the -I switch to give a path to the headers. The first would likely be -I../mylib/include, the second may be -I/home/user/local_libs/somelib/include.

The third one is a global installation, which should place them in /usr/local/include, but managed by a tool like automake or cmake. When packaging, the maintainer should adapt the installpath and/or the include path to install the headers to /usr/include.

When using automake you may have notices than the --prefix parameter defaults to /usr/local for a safe installation which does not interfere with system packages, while i.e. debian maintainers run ./configure --prefix=/usr in their package scripts. The include path is built from this prefix, so it follows the package installation.

Mimicking (but not duplicating) directory names

Generally we don't code in a vacuum and what we write is based upon what others have written before us. Assuming your C programs and associated header (.h) files are built upon another software system then you should model your directory structure after theirs.

Since I have no idea about your environment, lets take a common program and see what directory structure they used for their header files:

$ `gcc -print-prog-name=cc1plus` -v
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/5/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/5
 /usr/include/x86_64-linux-gnu/c++/5
 /usr/include/c++/5/backward
 /usr/lib/gcc/x86_64-linux-gnu/5/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed
 /usr/include
End of search list.

I have no special C or header libraries installed on my system so everyone should be able to replicate this search "out of the box".

When you drill down into: /usr/include/x86_64-linux-gnu/c++/5 you notice header files are included with C programs. So there is not hard and fast rule that headers have to be in their own directory.

When it comes to programming you can put files anywhere you want and call them anything you want. Of course whatever you decide, it should make sense to you and your co-workers.

Where header files are stored now

Check where header files are stored now:

$ locate *version.h*
/lib/firmware/carl9170fw/include/shared/version.h
/usr/include/linux/version.h
/usr/include/linux/dvb/version.h
/usr/include/x86_64-linux-gnu/gnu/libc-version.h
/usr/lib/python3/dist-packages/lxml/includes/lxml-version.h
/usr/lib/x86_64-linux-gnu/perl/5.22.1/CORE/git_version.h
/usr/src/linux-headers-3.16.53-031653/include/uapi/linux/dvb/version.h
/usr/src/linux-headers-3.16.53-031653/include/xen/interface/version.h
/usr/src/linux-headers-3.16.53-031653-generic/include/config/localversion.h
/usr/src/linux-headers-3.16.53-031653-generic/include/config/arch/want/compat/ipc/parse/version.h
/usr/src/linux-headers-3.16.53-031653-generic/include/config/isdn/diversion.h
/usr/src/linux-headers-3.16.53-031653-generic/include/generated/uapi/linux/version.h
/usr/src/linux-headers-4.10.0-28/include/uapi/linux/dvb/version.h
/usr/src/linux-headers-4.10.0-28/include/xen/interface/version.h
/usr/src/linux-headers-4.10.0-28-generic/include/config/localversion.h
/usr/src/linux-headers-4.10.0-28-generic/include/config/arch/want/compat/ipc/parse/version.h
/usr/src/linux-headers-4.10.0-28-generic/include/config/isdn/diversion.h
/usr/src/linux-headers-4.10.0-28-generic/include/generated/uapi/linux/version.h

This is just the top of my listing. It goes on extensively.

Based on existing header file locations, I would be inclined to create the directory:

/usr/include/ourcompany/

to store all the header (.h) files.

Consider the default search path

However as others have pointed out a popular location is:

/usr/local/include/

In this article written by Richard Stallman and others, they write:

By default, gcc searches the following directories for header files:

/usr/local/include/
/usr/include/

and the following directories for libraries:

/usr/local/lib/
/usr/lib/