Re: [linux_var] Strano codice C

To: linux_var - LUG di Varese e Provincia Mailing List <talking@ml.linuxvar.it>

Subject: Re: [linux_var] Strano codice C

From: Lorenzo Lobba <lorenzo.lobba@gmail.com>

Date: Wed, 23 May 2018 09:06:55 +0200

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Il giorno mar 22 mag 2018 alle ore 16:04 Salvatore Racano <salvatoreracano@gmail.com> ha scritto:

2018-05-22 15:32 GMT+02:00 Giovanni Orlandi <orlangio@gmail.com>:
Ciao,

in un file C di esempio ho trovato questo strano codice che mostro sotto:

#define handle_error(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)

A quanto capisco io il ciclo do { } while ( 0 ) viene eseguito sempre una sola volta,
ma a che cosa servirebbe ?
Forse ad evitare delle ottimizzazioni in sede di compilazione ?

Semplicemente per usare una macro come se fosse una funzione ed evitare che la macro una volta espansa crei effetti non voluti (Come detto da Salvatore).

Ad esempio, è buona cosa evitare di mettere ";" in fondo alla macro.

Nulla vieta di fare

#define A 4; ma meglio

#define A 4

Ciao,

Lorenzo

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References:

[linux_var] Strano codice C
- From: Giovanni Orlandi <orlangio@gmail.com>
Re: [linux_var] Strano codice C
- From: Salvatore Racano <salvatoreracano@gmail.com>