#ifndef DIRECTORY HEADERFILE not found

Question

How can I use directory in preprecessor command ifndef

EXAMPLE

#ifndef DIR/HEADERFILE_H #include "dir/headerfile.h" #endif

Use a character the preprocessor allows? #ifndef DIR_HEADERFILE_H — Simon Kraemer
– Simon Kraemer, Commented Nov 7, 2016 at 13:43
What are you trying to achieve? The preprocessor understands text - not directory structures? Once a file has been #includedd it doesn't then have the filename/directory #defined. — doctorlove
– doctorlove, Commented Nov 7, 2016 at 13:50
IT IS VERY INTERESTING, WHY I AM GETTING -2? SOME COMMENTS FIRST? — Dušan Tichý
– Dušan Tichý, Commented Nov 7, 2016 at 14:07

Community · Accepted Answer · 2017-05-23 12:10:54Z

To answer the specicif question, you cannot use a directory in a preprocessor command like #ifndef.

The include guards in the header file often take the form

#ifndef DIRECTORY_HEADERFILE_INCLUDED #define DIRECTORY_HEADERFILE_INCLUDED //.... contents #endif

To include the header, then simple use

#include "dir/headerfile.h"

A long while ago some people suugested a double include guard, or redundant include guard, wherein you checked before the #include line to speed things up, as mentioned in this question. The c2 wiki has some further information esp.

"Good compilers make this idiom unnecessary. "

In either case the tendacny is to use _ instead of /, to form a valid macro.

Community · Accepted Answer · 2017-05-23 10:33:00Z

As explained in this question, only alphanumeric characters and underscores (a-z, A-Z, 0-9, and _) are allowed for macro and constants names. You can define your own constant replacing / with _:

#ifndef DIR_HEADERFILE_H

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