On 31/05/17 01:23, Vincent Lefevre wrote:
> On 2017-05-30 23:04:02 +0200, Florian Weimer wrote:
>> * Vincent Lefevre:
>>
>>> Is it normal that -std=c90 -pedantic-errors allows to use
>>>
>>> #include <stdint.h>
>>>
>>> ?
>>
>> Yes. It's difficult where to draw the line. <inttypes.h> was
>> apparently available with some C90 compilers, so it would make sense
>> to allow it in C90 mode. But this means that it wouldn't be
>> completely out of line to accept <stdint.h>, too.
I have used C90 compilers that provided a <stdint.h> too.
And since C90 does not define a <stdint.h>, an implementation or user is
free to put a file called "stdint.h" in a directory that is searched for
system includes - a compiler cannot arbitrarily blacklist a header name
in a standard that does not mention that name!
>
> Now, what actually mattered in my case was the use of (u)intmax_t.
> For instance, consider the following program:
>
> #include <stdio.h>
> #include <stdint.h>
> #include <limits.h>
>
> int main (void)
> {
> uintmax_t i = -1;
> printf ("%d\n", i > ULONG_MAX);
> return 0;
> }
>
> In C90, "long" is the largest type, so that one should always expect
> the output 0. But:
"long" is the largest standards-mandated type in C90, but it is not
necessarily the largest type available. An implementation is allowed to
provide additional types, even in "pedantic" C90 mode.
In this particular case, uintmax_t is defined using the "__extension__"
keyword inside the <stdint.h> file. (At least, that is the case in my
sample <stdint.h> here.) The implementation is allowed to do that - the
identifier "__extension__" is reserved for the implementation, and the
compiler can use it however it wants.
So in C90 mode, <stdint.h> is not standardised and can contain whatever
the implementation (or user) wants. The same applies to the type
"uintmax_t" - C90 says nothing about it. You have no guarantees, and
the working of the code depends entirely on the contents of <stdint.h>.
If you want to stick to C90, and you want to have a uintmax_t that
matches "long", then I suggest you don't include headers that are not
relevant for C90, and define the types yourself. Perhaps start with:
#ifdef __STRICT_ANSI__
typedef long int intmax_t;
typedef unsigned long int uintmax_t;
#else
#include <stdint.h>
#endif
>
> cventin:~> gcc -std=c90 -pedantic-errors -o tst tst.c -m32
> cventin:~> ./tst
> 1
>
> under GNU/Linux.
>
> IMHO, at least some features of <stdint.h> should yield a warning
> with -pedantic (an error with -pedantic-errors).
>
