Including headers

Quotes or chevrons ?

In C, there is two ways to include a header :

#include "header.h"

#include <header.h>

There is one technical difference : only the inclusion with "" searches for the header in the same directory as the current file (without the need to add a -I compiler flag or edit an environment variable).

So in the case of a private header, i.e. one in the src folder alongside the sources (as opposed to one in the include folder), there is a technical reason to use "" to include :

#include "private.h"

The rest of the time, either way of including could technically be used. So the following rule is an arbitrary convention :

When including a header, use "" if that header is in the same git repository, else use <>

So that means that when in o2s/string.h we are including o2s/array.h and stddef.h, we write:

#include "o2s/array.h"
 
#include <stddef.h>

Order

While any inclusion order would do, going from most to least specific has an advantage: If someone were to write a header like o2s/array.h, using the type bool but forgetting to include stdbool.h, then as long as all source files that include o2s/array.h also include (directly or not) stdbool.h above, the omission would remain unnoticed.

So the convention here is something like :

/* Source specific header */
#include "private.h"
 
/* Project specific public headers */
#include "o2s/deque.h"
#include "o2s/string.h"
 
/* Linux specific headers */
#include <fcntl.h>
#include <termios.h>
 
/* Standard C headers */
#include <errno.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

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