How to use C89 with certain C99 features

[richardcavell@mail.com]

I'm writing an open source project that is designed to run on all kinds 
of obscure architectures. My project relies on libcurl, which is in C89 
and very portable. I don't want to limit the users' choice of compiler 
unnecessarily. So, for example, I use malloc instead of variable length 
arrays. Having said that, using long string literals seems pretty 
harmless and I can't figure out a way to avoid usage of the other three 
C99 features while retaining their functionality.

Richard

-----Original Message-----
From: David Brown <david@westcontrol.com>
To: gcc-help@gcc.gnu.org
Sent: Tue, Apr 5, 2011 8:47 pm
Subject: Re: How to use C89 with certain C99 features

On 05/04/2011 12:32, richardcavell@mail.com wrote:
> Hi, everyone. I'm building a project in C. My idea is that I want it 
to
> be mostly C89, except that I will be using certain features of C99. 
What
> compiler flags do I need to tell GCC what I want?
>

What are you actually trying to achieve?  The only reason I can think 
of
for someone to write C89 standard is to be compatible with more limited
or older compilers.  If that's the case, then you should write C89 - 
not
C99.  Many compilers that are basically C89 (or C90, or ANSI) will
accept a few C99 features, such as // comments.  But they are very
unlikely to accept more complex C99 features, such as newer ways to
handle variadic parameters.  Thus your code will only work with a 
proper
C99 compiler, and thus might as well use --std=c99.



> At present, if I compile with -std=c99, I get no errors or warnings at
> all. If I compile with -std=c89, I get the following warnings:
>
> (When I use macros with ... and __VA_ARGS__)
> warning: anonymous variadic macros were introduced in C99
>
> (When I use long string literals)
> warning: string length '613' is greater than the length '509' ISO C90
> compilers are required to support
>
> (When I use vsnprintf)
> warning: implicit declaration of function 'vsnprintf'
>
> (When I initialize a struct with run-time data)
> warning: initializer element is not computable at load time
>
> Richard
>
>