Should GCC warn when __LINE__ is treated as %u %d %i?
Tue Feb 19 15:21:00 GMT 2019
On 2/19/19 4:27 AM, Jonny Grant wrote:
> On 18/02/2019 22:03, Martin Sebor wrote:
>> On 2/17/19 7:12 AM, Jonny Grant wrote:
>>> **Please keep my email address in any replies.
>>> 1) should this not give type conversion warnings?
>>> printf("lineoutput %d:%u:%i\n", __LINE__, __LINE__, __LINE__);
>>> 2) Should __LINE__ expand as an 'int', or 'unsigned int'?
>>> Had expected line 9 to expand as '9U', but -save-temps shows it ends
>>> up as:
>>> printf("lineoutput %d:%u:%i\n", 9, 9, 9);
>> The bigger problem with __LINE__ is that it need not expand to int
>> at all, such as in the following:
>> $ cat u.c && gcc -O2 -S -Wall -Wextra u.c
>> #line 2147483647
>> void f (void)
>> Â Â __builtin_printf ("%i", __LINE__);
>> u.c: In function âfâ:
>> u.c:-2147483646:21: warning: format â%iâ expects argument of type
>> âintâ, but argument 2 has type âlong intâ [-Wformat=]
>> Notice how the line number in the message doesn't correspond to
>> the sum of 2147483647 and 3 (the offset from the #line directive).
> Good point. Looks like a compiler limitation. Although I wonder how many
> files really have that many lines, but anyway...
> GCC could store the line number as a 'long int', then can display line
> numbers up to 2^63
> u.c: In function âfâ:
> u.c:2147483650:21: warning: format â%iâ expects argument of type âintâ,
> but argument 2 has type âlong intâ [-Wformat=]
> I can file a on gcc.gnu.org bugzilla, or would you prefer to file yourself?
You're right that having that many physical lines is very unlikely.
The only way for this to be noticed that I can think of is in
conjunction with the #line directive explicitly setting very large
numbers (perhaps in generated code). I'm not sure it's worth growing
the GCC internal tree node by 4 bytes but detecting the overflow and
issuing a diagnostic, maybe even an error, rather than allowing line
numbers to start to decrease, would be cheap and an improvement.
Either way, if you agree this is worth at least making a record of
in Bugzilla, please go ahead.
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