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HACKING: document #include order

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It was not obvious to me why "qemu/osdep.h" must be the first #include.
This documents the rationale and the overall #include order.

Cc: Fam Zheng <famz@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1479307161-24658-1-git-send-email-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2016-11-16 14:39:21 +00:00
parent dbe2b65566
commit 0891ee1112
1 changed files with 18 additions and 0 deletions
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@ -1,10 +1,28 @@
1. Preprocessor 1. Preprocessor
1.1. Variadic macros
For variadic macros, stick with this C99-like syntax: For variadic macros, stick with this C99-like syntax:
#define DPRINTF(fmt, ...) \ #define DPRINTF(fmt, ...) \
do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0) do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
1.2. Include directives
Order include directives as follows:
#include "qemu/osdep.h" /* Always first... */
#include <...> /* then system headers... */
#include "..." /* and finally QEMU headers. */
The "qemu/osdep.h" header contains preprocessor macros that affect the behavior
of core system headers like <stdint.h>. It must be the first include so that
core system headers included by external libraries get the preprocessor macros
that QEMU depends on.
Do not include "qemu/osdep.h" from header files since the .c file will have
already included it.
2. C types 2. C types
It should be common sense to use the right type, but we have collected It should be common sense to use the right type, but we have collected