How to include header files without quotation marks?

Question

I'm kind of new to programming so please go easy on me. Anyways, I know about including header files that you, yourself, have defined. For example:

#include "yourHeader.h"

I'm trying to use FLTK for its GUI options, however, many of its header files include other header files using an include like this:

#include <FL/Blah.h>

instead of this:

#include "FL/Blah.h"

I would have to go every header file that has the include in angle brackets and change them to quotation marks for them to work. I am currently working in CodeBlocks right now, if that matters. Is there any way to include the header files using angle brackets instead of quotation marks, or am I stuck with having to go into the header files themselves and manually swapping them all out?

Answer 1

Generally， the header file from

#include "headerfile"

will searched in the current source path. If the search fails, it is reprocessed as if

#include <header file>

does.

Your FLTK library is using include like the following?

#include <FL/Blah.h>

The FL's parent path should be in the predefined INCLUDE path. You may edit you Makefile or project settings.

Answer 2

You can add the folder which contains all your headers to your include path while compiling. How to add a default include path for GCC in Linux?

Answer 3

Some background

Ok there are two set of include search path.

The user include path:
This is usually only the current directory (also known as ".").
Note: It may be others but for simplicity lets just use "." in the examples below.

Then there is the system include path:
This is usually a few places in your machines (could be /usr/include and /usr/local/include).
Note: It may be others but for simplicity lets just assume these in the examples below.

How it usually works.

There are caveats and not all compilers work exactly the same. But the following are a good rules of thumb.

When you include a file using quotes "".

#include "yourHeader.h"

It will search for this file in all the directories specified in the "user include path". If it fails to find them there it will then look in all the directories specified by the "system include path". So your compiler will search for the following files:

./yourHeader.h
/usr/include/yourHeader.h
/usr/local/include/yourHeader.h

It will use the first one it finds.

When you use the <> in the include:

#include <FL/Blah.h>

It will search for the files in the "system include path" first. Then depending on your compiler may optionally search the "user include path" (but lets assume not for now).

So in this case it will search for the files:

/usr/include/FL/Blah.h
/usr/local/include/FL/Blah.h

It will use the first one it finds.

Modifying the Default

So these are the default paths that will be searched for a file. But your compiler will allow you to add extra paths to both of these search paths (usually). It depends on your compiler how to add search paths.

For gcc (and probably clang) it uses -I and -isystem (and probably more)

Expectations.

When you see <> in the include header it usually means this is an already installed library that you are looking for. So your code assumes that the FLTK library has already been installed on your machine.

When you see "" in the include header you should assume that it is a local file that belongs to the project.