How to tell g++ compiler where to search for include files?

Question

In a "working directory" I have a lot of *.cpp and *.h files that `#include` each other and files from subdirectories. For example: ``` #include "first.h" #include "second.h" #include "dir1/third.h" #include "dir2/fourth.h" ``` In my own directory (that is different from the "working" directory) I would like to create a new *.cpp and *.h file that includes one of the files from the "working" directory. For example: ``` #include "/root/workingdirectory/first.h" ``` However, it does not work. Because "first.h" might include "second.h" and "second.h" is not located in my directory. Is there a way to tell the compiler that it needs to search included files not in the current but in the working directory: `/root/workingdirectory/`? To make it even more complex, `dir1` and `dir2` are not located in my working directory. They are located in `/root/workingdirectory2/`. So, my second question is if it is possible to resolve this problem by letting compiler know that subdirectories are located…

Accepted Answer

As you've already been told, it's useful to read the manual - specifically this chapter - and even more specifically right here. Specifically, you want ``` g++ -I/root/workingdirectory -I/root/workingdirectory2 ``` Note also the documentation on `#include` directive syntax, described here as: 2.1 Include Syntax Both user and system header files are included using the preprocessing directive `#include`. It has two variants: ``` #include ``` This variant is used for system header files. It searches for a file named file in a standard list of system directories. You can prepend directories to this list with the -I option (see Invocation). ``` #include "file" ``` This variant is used for header files of your own program. It searches for a file named file first in the directory containing the current file, then in the quote directories and then the same directories used for ``. You can prepend directories to the list of quote directories with the -iquote option. The argument of `#include`, whether delimited with quote marks or angle brackets, behaves like a string constant in that comments are not recognized, and macro names are not expanded. Thus,`#include ` specifies inclusion of a system header file named x/*y. However, if backslashes occur within file, they are considered ordinary text characters, not escape characters. None of the character escape sequences appropriate to string constants in C are processed. Thus, `#include "x \y"` specifies a filename containing three backslashes. (Some systems interpret `\` as a pathname separator. All of these also interpret `/` the same way. It is most portable to use only `/`.) It is an error if there is anything (other than comments) on the line after the file name. So for example ``` #include "first.h" ``` will start looking in the same directory as the .cpp file containing this directive (or take a relative path as relative to this directory). If you want to use the include path (specified by `-I`) you should use ``` #include ``` Usual practice is to use the `#include "local.h"` form for headers inside a library/package/module (however you've chosen to organize that), and the `#include ` form for headers from external/3rd-party or system libraries.

How to tell g++ compiler where to search for include files?

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