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Re: Error message for a dangling pointer

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On 07/02/17 16:07, BartC wrote:
> On 07/02/2017 02:02, Keith Thompson wrote:
>> ram@zedat.fu-berlin.de (Stefan Ram) writes:
>>>   For teaching purposes, I just wrote this program to show
>>>   dangling pointers:
>>>
>>> #include <stdio.h>
>>> int main( void )
>>> { int * p;
>>>   { int i = 27; p = &i; }
>>>   printf( "%d\n", *p ); }
>>
>> (A side note: Your students might later have difficulties with more, um,
>> conventional C code layouts.)
>>
>>>   I hope you all agree that »p« in the last line /is/
>>>   a dangling pointer.
>>
>> Yes.
>>
>>>   The error message and output is not what I expected,
>>>   but still interesting:
>>>
>>> main.c: In function 'main':
>>> main.c:6:3: warning: 'i' is used uninitialized in this function
>>> [-Wuninitialized]
>>>    printf( "%d\n", *p ); }
>>>    ^
>>> main.c:5:9: note: 'i' was declared here
>>>    { int i = 27; p = &i; }
>>>          ^
>>> 0
>>>
>>>   »i« /was/ initialized in the program,
>>>   so the error message is not accurate.
>>>
>>>   (I do not write »misleading«, since it is so
>>>   obviously wrong that it won't mislead anyone.)
>>
>> I get that message with gcc 6.3.0, and with a gcc snapshot from
>> 2017-01-12 that claims to be gcc 7.0.0, but not with gcc 6.2.0
>> (or with clang).
> 
> I couldn't get any diagnostic with any compiler. That included gcc 5.1.x
> and 6.2.x with all warnings turned on.
> 

Testing with <https://gcc.godbolt.org/> I get that for gcc 5 onwards
(including 6.2 and 5.1), but not clang.

However, like many warnings you need to have optimisation enabled so
that gcc will do more analysis of the code.

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Re: Error message for a dangling pointer Keith Thompson <kst-u@mib.org> - 2017-02-06 18:02 -0800
  Re: Error message for a dangling pointer BartC <bc@freeuk.com> - 2017-02-07 15:07 +0000
    Re: Error message for a dangling pointer David Brown <david.brown@hesbynett.no> - 2017-02-07 16:24 +0100

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