Revisions to Why use do { } while (0) in macro definition? [duplicate]

replaced http://stackoverflow.com/ with https://stackoverflow.com/

edited May 23, 2017 at 12:34

URL Rewriter Bot

Possible Duplicate:
Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?

I met code like below:

#define ev_io_init(ev,cb,fd,events) \ do { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ } while (0)

I want to know why the author use do { } while (0) here. Is there any difference with this?

#define ev_io_init(ev,cb,fd,events) { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ }

BTW: the code is from libev, ev_local.h

Possible Duplicate:
Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?

I met code like below:

#define ev_io_init(ev,cb,fd,events) \ do { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ } while (0)

I want to know why the author use do { } while (0) here. Is there any difference with this?

#define ev_io_init(ev,cb,fd,events) { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ }

BTW: the code is from libev, ev_local.h

Possible Duplicate:
Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?

I met code like below:

#define ev_io_init(ev,cb,fd,events) \ do { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ } while (0)

I want to know why the author use do { } while (0) here. Is there any difference with this?

#define ev_io_init(ev,cb,fd,events) { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ }

BTW: the code is from libev, ev_local.h

CPP macros have their own tag. macros wiki states: "questions relating to other macro programming languages should not use this tag"

Link

edit approved Mar 30, 2015 at 12:20

a3f

8.7k
1
43
47

c macros c-preprocessor libev

reinserted duplicate post notice that was removed in last edit

Source Link

edited Jan 10, 2013 at 11:14

Linus Kleen

34.8k
10
97
100

Possible Duplicate:
Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?

I met code like below:

#define ev_io_init(ev,cb,fd,events) \ do { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ } while (0)

I want to know why the author use do { } while (0) here. Is there any difference with this?

#define ev_io_init(ev,cb,fd,events) { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ }

BTW: the code is from libev, ev_local.h

I met code like below:

#define ev_io_init(ev,cb,fd,events) \ do { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ } while (0)

I want to know why the author use do { } while (0) here. Is there any difference with this?

#define ev_io_init(ev,cb,fd,events) { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ }

BTW: the code is from libev, ev_local.h

Possible Duplicate:
Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?

I met code like below:

#define ev_io_init(ev,cb,fd,events) \ do { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ } while (0)

I want to know why the author use do { } while (0) here. Is there any difference with this?

#define ev_io_init(ev,cb,fd,events) { \ ev_init ((ev), (cb)); \ ev_io_set ((ev),(fd),(events)); \ }

BTW: the code is from libev, ev_local.h

this is not interpreted by the preprocessor as a macro now that it's spread over multiple lines without escaping

Source Link

edit approved Feb 29, 2012 at 9:32

strcat

5.7k
2
31
31

Loading

insert duplicate link

Source Link

edited Feb 29, 2012 at 8:52

Community Bot

1
1

Loading

Post Closed as "exact duplicate" by Greg Hewgill, Alok Save, Nim, CommunityBot, Gunther Piez

Why use apparently meaningless do-while and if-else statements in macros?

occurred Feb 29, 2012 at 8:52

fixed code formatting

Source Link

edited Feb 29, 2012 at 8:48

Quasdunk

15.2k
3
39
47

Loading

Source Link

asked Feb 29, 2012 at 8:45

ciphor

8.3k
11
57
71

Loading

Collectives™ on Stack Overflow

Return to Question