questions about C language dialects in Xcode and C standards in general

Tron55555 wrote:
1.) What's up with the Compiler Default option?

Xcode always uses the same compiler (GCC, right?) no matter what computer it's on, so shouldn't the Compiler Default setting be the same on any computer?

2.) There are two seemingly identical options: ANSI C and C89. Technically, of course, any ANSI C standard (C89 or C99) could be considered ANSI C, but specifically, the term ANSI C is used to refer to the C89 standard -- I've read from numerous sources ("Learn C on the Mac" is the one I have in front of me at the moment). So, then, what would be the difference between the ANSI C dialect option and the C89 dialect option?

3.) What's the deal with the ISO standard (C90) not being included in these options? Is it just similar enough to either C89 or C99 that they didn't feel it was necessary to include, or is there some other reason?

4.) With the exception of Compiler Default and the ANSI C options, each option has a GNU version. So, in addition to the C89 dialect option, they also have the GNU89 dialect option, and in addition to the C99 dialect option, they also have the GNU99 dialect option. These (GNU89 and GNU99) aren't actual established standards like C89 and C99, are they? I assume they are just options for the dialect. So, what are they? What's the difference between them and their C counterparts (GNU89 vs. C89 and GNU99 vs. C99)?

5.) How exactly do these options affect your project, or your code in specific. For example, I believe C++-style comments (the // comments) weren't brought into the C standard until C99. I think this is correct, but whether it is or not, let's assume it is for the sake of this question. So, I'm guessing that if I set the C Language Dialect option to C99 and try to use a C++ comment then all will be well, but if I set the option to C89 and try the same thing then I will get an error -- is this right? I would test it myself, but like I said, I'm not positive that I'm correct about C++ comments being introduced to the standard with C99.

So, if this is right, then you'll be more restricted with your code by setting the option to C89 than you would be by setting it to C99, right? So if I wrote code with the option set to C99 and used some of the features of language that were added to the C standard with C99 and not before that, it would work fine, but if I then needed to give the code to someone else for them to edit it, and if they were using a compiler that used to original ANSI C (C89) standard, then they would get a bunch of errors and have to edit the code, right?

For this reason, might it be a good idea for me to get in the habit of programming C with the language dialect option set to C89 (or ANSI C -- again, not sure why both are there or what the difference is).

6.) I'm not really clear on exactly what a standard actually is or what it does in terms of the C language. When they establish a new standard for the C language, what exactly happens to the language? Does the language itself actually change? Do they change the built-in language elements (the syntax and structure and keywords and all that) to correspond to the new standard? Or is it more of just a declaration of how people are supposed to program C under the standard? I'm not sure if that made sense, but I just wanted to try to understand the nature of standards for the C language a little better and how, exactly, they contribute to or alter the language.

7.) Does anyone know if there's been any talk of a new standard, or are we going to be under the C99 standard for the foreseeable future? Being a more low-level language, maybe C is more self-sufficient and they don't feel the need to make changes to the languageOr maybe that makes no sense.

Tron55555 wrote:
Oh well. Would you recommend Intel's compiler?

Are there any advantages for a simple soul like myself?

So then, now ANSI C is identical to C99?

Yeah I understood that, but I'm still not getting why they didn't include C90. Are you saying it was because C90 is ISO? Do they not include ISO standards? Why is that?

I actually tried to answer that in my post ("I would test it myself, but like I said, I'm not positive that I'm correct about C++ comments being introduced to the standard with C99" -- me). In other words, they could have both not worked, and that could have only been because I was wrong about C++ comments not being added to the standard until 1999. I'm sure I can look that up somewhere, though (I tried briefly before the last post, but I guess not enough).

#include <stdio.h>
int main(void)
 {
 // This is a comment.
 return 0;
 }

Okay -- good explanation. Without taking much more of your time, what is BSD-only code?

Don't look it up, test it.

#include <stdio.h>
int main(void)
 {
 // This is a comment.
 return 0;
 }

gcc -std=c89 test.c
gcc -std=c99 test.c
gcc test.c

cc -std=c89 -pedantic -fsyntax-only test.c
$ cc -std=c89 -pedantic -fsyntax-only test.c 
std.c: In function ‘main’:
std.c:5: error: syntax error before ‘/’ token
$ cc -std=c99 -pedantic -fsyntax-only test.c 

 -pedantic
 Issue all the warnings demanded by strict ISO C and ISO C++; reject
 all programs that use forbidden extensions, and some other programs
 that do not follow ISO C and ISO C++. For ISO C, follows the
 version of the ISO C standard specified by any -std option used.
...
 Some users try to use -pedantic to check programs for strict ISO C
 conformance. They soon find that it does not do quite what they want:
 it finds some non-ISO practices, but not all---only those for which
 ISO C requires a diagnostic, and some others for which diagnostics
 have been added.
...

int i;
for(i = 0; i < 10; ++i)
 {
 int j;
 int k;
 int q;
 // do something with j.
 // do something with k.
 // do somethign with q.
 }

for(int i = 0; i < 10; ++i)
 {
 // do something with j.
 int j;
 // do something with k.
 int k;
 // do somethign with q.
 int q;
 }

Tron55555 wrote:
So then what is the difference between "-std=c99" and "-ansi"?

Why would someone set there project settings to one over the other?

I assumed C90 added things to the language that C89 didn't have.

I know you had to declare your variables at the beginning before C99, but at the beginning of what? Every block of code? Is that right?

Tron55555 wrote:
So then what's the difference between "-std=c89" and "-ansi"?

Really? That's interesting. I thought it was supposed to be most efficient to declare a variable within the smallest scope possible.

So, you're saying even if a variable was never going to be used outside a certain "if" construction, I should still declare it at the beginning of the function?