Variables are accepted as the subscription when declare a array

[lovecreatesbeauty]

It is strange. Happen to get following the fragment compiled
successfully. Is there anything wrong with my compiler or my mind?

Please guide me to correct my understanding on it.

Sincerely,

lovecreatesbeauty


$ cat p113.c
int main(void)
{
int len = 100;
int a[len];
}
$ gcc --version
gcc (GCC) 4.1.0
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is
NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

$ gcc -std=c89 p113.c
$ gcc -std=c99 p113.c
$

 

[Keith Thompson]

It is strange. Happen to get following the fragment compiled
successfully. Is there anything wrong with my compiler or my mind?

Please guide me to correct my understanding on it.

$ cat p113.c
int main(void)
{
int len = 100;
int a[len];
} [...]

$ gcc -std=c89 p113.c
$ gcc -std=c99 p113.c
$

gcc isn't a conforming compiler unless you ask it nicely to act as
one.

% gcc -std=c89 p113.c
% gcc -std=c89 -pedantic p113.c
p113.c: In function `main':
p113.c:4: warning: ISO C90 forbids variable-size array `a'
%

 

[Kenneth Brody]

It is strange. Happen to get following the fragment compiled
successfully. Is there anything wrong with my compiler or my mind?

Please guide me to correct my understanding on it.

$ cat p113.c
int main(void)
{
int len = 100;
int a[len];
}

[...]
gcc isn't a conforming compiler unless you ask it nicely to act as
one.

% gcc -std=c89 p113.c
% gcc -std=c89 -pedantic p113.c
p113.c: In function `main':
p113.c:4: warning: ISO C90 forbids variable-size array `a'

[...]

Is it really non-conforming? Are variable-sized arrays "forbidden", or
is it not part of the standard, but allowable as an extension?

--
+-------------------------+--------------------+-----------------------------+
| Kenneth J. Brody | www.hvcomputer.com | |
| kenbrody/at\spamcop.net | www.fptech.com | #include <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------------+
Don't e-mail me at: <mailto:[email protected]>

 

[Robert Gamble]

It is strange. Happen to get following the fragment compiled
successfully. Is there anything wrong with my compiler or my mind?

Please guide me to correct my understanding on it.

$ cat p113.c
int main(void)
{
int len = 100;
int a[len];
}

[...]
gcc isn't a conforming compiler unless you ask it nicely to act as
one.

% gcc -std=c89 p113.c
% gcc -std=c89 -pedantic p113.c
p113.c: In function `main':
p113.c:4: warning: ISO C90 forbids variable-size array `a'

[...]

Is it really non-conforming? Are variable-sized arrays "forbidden", or
is it not part of the standard, but allowable as an extension?

c89 draft
3.5.4.2 Array Declarators:
Constraints:
The expression that specifies the size of an array shall be an integral
constant expression that has a value greater than zero.

The program is non-conforming. A conforming implementation must
provide a diagnostic but may then continue to do what ever it likes as
the behavior is no longer defined.

Robert Gamble