Is main a registered word

[small TUX]

Hello programmers;
I joinded today itself. Can anyone say
about the word main, is it a registered word, justify your question
also. I would like to point about one thing that we can make variables
with name main.
Thanks.

[Eric Sosman]

small TUX wrote:

Hello programmers;
I joinded today itself. Can anyone say
about the word main, is it a registered word, justify your question
also. I would like to point about one thing that we can make variables
with name main.

`main' is not a keyword, and `main' is not a reserved
identifier. It is possible (although perverse) to use `main'
as the name of a macro, or of a variable, or of a struct or
union tag, or ...

#include <stdio.h>
int main(void) {
const char *main = "world";
printf ("Hello, %s!\n", main);
#define main 0
return main;
}

(Not recommended.)

--
Eric Sosman
es*****@acm-dot-org.invalid

[Simias]

Eric Sosman <es*****@acm-dot-org.invalidwrit es:

small TUX wrote:

>Hello programmers;
I joinded today itself. Can anyone say
about the word main, is it a registered word, justify your question
also. I would like to point about one thing that we can make variables
with name main.

`main' is not a keyword, and `main' is not a reserved
identifier. It is possible (although perverse) to use `main'
as the name of a macro, or of a variable, or of a struct or
union tag, or ...

#include <stdio.h>
int main(void) {
const char *main = "world";
printf ("Hello, %s!\n", main);
#define main 0
return main;
}

(Not recommended.)

And what about calling main as a regular function?
e.g.:

#include <stdio.h>

int main(void)
{
printf("hello") ;
main();
return (0);
}

It makes an infinite recursion with gcc, but i think i've heard that you
can't call main, so is this an undefined behaviour?

--
Simias
email rot13-ified

[Richard Tobin]

In article <86************ @simias.hd.free .fr>,
Simias <fv******@tznvy .pbzwrote:

>It makes an infinite recursion with gcc, but i think i've heard that you
can't call main, so is this an undefined behaviour?

No, it's perfectly legal to call main().

I can't think of any cases where it wouldn't be clearer to instead
call another function though. main()'s arguments are intended to be
convenient for accessing command line arguments, and that's unlikely
to be a useful internal interface.

-- Richard


--
"Considerat ion shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.

[Eric Sosman]

Simias wrote:

[...]
And what about calling main as a regular function?
e.g.:

#include <stdio.h>

int main(void)
{
printf("hello") ;
main();
return (0);
}

It makes an infinite recursion with gcc, but i think i've heard that you
can't call main, so is this an undefined behaviour?

The sample you show is valid C, but it expresses a program
that does not terminate in any normal fashion. It is likely to
exceed an implementation limit (two limits, actually, but the
problems of generating an infinitely long line of text aren't
immediately relevant to your question) and terminate abnormally.

It is possible to call main recursively, if (as with any
other recursive function) you arrange for the recursion to
"bottom out" eventually. Here is a silly program that prints
its command-line arguments in reverse order:

#include <stdio.h>
int main(int argc, char **argv) {
if (argc 0) {
main (argc-1, argv+1);
puts (*argv);
}
return 0;
}

--
Eric Sosman
es*****@acm-dot-org.invalid

[mark_bluemel]

small TUX wrote:

Hello programmers;
I joinded today itself.

(UK readers, can you hear Bluebottle saying that as well?)

Can anyone say
about the word main, is it a registered word,

Yes of course someone can and the answer is no it isn't.

http://c-faq.com/ansi/avail.html led me to the draft ANSI C89 standard
document which explains that on a "hosted environment" the function
called at program startup is called "main", it returns an int value and
either takes no parameters or 2 parameters (it also defines what these
parameters are).

So "main" is just a function name which has a specific use in hosted
environments. Nothing more, nothing less.

justify your question also.

I don't have a question, so why do I need to justify it?

[Thad Smith]

ma**********@po box.com wrote:

http://c-faq.com/ansi/avail.html led me to the draft ANSI C89 standard
document which explains that on a "hosted environment" the function
called at program startup is called "main", it returns an int value and
either takes no parameters or 2 parameters (it also defines what these
parameters are).

So "main" is just a function name which has a specific use in hosted
environments. Nothing more, nothing less.

In C99, executing to the closing brace of main is the equivalent of
return 0.

--
Thad

[Simias]

Thad Smith <Th*******@acm. orgwrites:

ma**********@po box.com wrote:
In C99, executing to the closing brace of main is the equivalent of
return 0.

Even if it's a recursive call to main?

--
Simias
email rot13-ified

[Keith Thompson]

Simias <fv******@tznvy .pbzwrites:

Thad Smith <Th*******@acm. orgwrites:

>ma**********@po box.com wrote:
In C99, executing to the closing brace of main is the equivalent of
return 0.

Even if it's a recursive call to main?

I think so.

C99 5.1.2.2.3 says:

If the return type of the main function is a type compatible with
int, a return from the initial call to the main function is
equivalent to calling the exit function with the value returned by
the main function as its argument; reaching the } that terminates
the main function returns a value of 0.

The way it's phrased, I think the last clause refers to any call to
main, not just the initial call.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[santosh]

Keith Thompson wrote:

Simias <fv******@tznvy .pbzwrites:

Thad Smith <Th*******@acm. orgwrites:

ma**********@po box.com wrote:
In C99, executing to the closing brace of main is the equivalent of
return 0.

Even if it's a recursive call to main?

I think so.

C99 5.1.2.2.3 says:

If the return type of the main function is a type compatible with
int, a return from the initial call to the main function is
equivalent to calling the exit function with the value returned by
the main function as its argument; reaching the } that terminates
the main function returns a value of 0.

The way it's phrased, I think the last clause refers to any call to
main, not just the initial call.

It seems to contradict the preceding statement. Anyhow, what if the
code returns a value other than zero, say EXIT_FAILURE?

I suppose the last statement is meant for the situation where main() is
prototyped as returning an int value, but the code itself fails to
return an explicit value, terminating by just a return.