gcc warnings

gcc warnings

[kamelopardus]

Hello.

I use gcc 3.4.2 under mingw32. I need to put compiler warnings about
uninitialized variables into some text file, for example, "warnings.txt".

i try 

gcc -O -Wuninitialized -v echo.c>warnings.txt

after the execution i can see warnings on the screen, but file
"warnings.txt" is empty.

Can anyone advise, where am i wrong?



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Re: gcc warnings

[Andrew Bell]

On Tue, Aug 12, 2008 at 10:25 AM, kamelopardus <killorn@yandex.ru> wrote:
>
> Hello.
>
> I use gcc 3.4.2 under mingw32. I need to put compiler warnings about
> uninitialized variables into some text file, for example, "warnings.txt".
>
> i try
>
> gcc -O -Wuninitialized -v echo.c>warnings.txt

They are going to stderr, not stdout.  Try:

gcc -O -Wuninitialized -v echo.c 2>& > warnings.txt

-- 
Andrew Bell
andrew.bell.ia@gmail.com

Re: gcc warnings

[Joel Dice]

On Tue, 12 Aug 2008, Andrew Bell wrote:

> On Tue, Aug 12, 2008 at 10:25 AM, kamelopardus <killorn@yandex.ru> wrote:
>>
>> Hello.
>>
>> I use gcc 3.4.2 under mingw32. I need to put compiler warnings about
>> uninitialized variables into some text file, for example, "warnings.txt".
>>
>> i try
>>
>> gcc -O -Wuninitialized -v echo.c>warnings.txt
>
> They are going to stderr, not stdout.  Try:
>
> gcc -O -Wuninitialized -v echo.c 2>& > warnings.txt

I think you mean:

gcc -O -Wuninitialized -v echo.c > warnings.txt 2>&1

Re: gcc warnings

[kamelopardus]

Andrew Bell wrote:
> 
> On Tue, Aug 12, 2008 at 10:25 AM, kamelopardus <killorn@yandex.ru> wrote:
>>
>> Hello.
>>
>> I use gcc 3.4.2 under mingw32. I need to put compiler warnings about
>> uninitialized variables into some text file, for example, "warnings.txt".
>>
>> i try
>>
>> gcc -O -Wuninitialized -v echo.c>warnings.txt
> 
> They are going to stderr, not stdout.  Try:
> 
> gcc -O -Wuninitialized -v echo.c 2>& > warnings.txt
> 
> -- 
> Andrew Bell
> andrew.bell.ia@gmail.com
> 
> 


It worked, thanks.
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gcc warnings

[Humpolicek, Jiri - Acision]

Hi,
            I have, from my point of view, strange problem. I want to tell gcc to report all compilation warnings, especially warnings about assigment from variable of greater type to variable with smaller type. For example, when I write following code and compile it with next command no warning is reported:

c++ -o test test.cpp -Wall -Wextra -Wconversion -pedantic

#include "stdio.h"

int main()
{
        long a = 10000;
        unsigned char b = a;

        printf("%d\n", b);

        return b;
}

Gcc -v prints these information, but I have already test it on different versions but with same unsatsfactory results:

Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.1.2/work/gcc-4.1.2/configure --prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.1.2 --includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include --datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2 --mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2/man --infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2/info --with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include/g++-v4 --host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec --enable-nls --without-included-gettext --with-system-zlib --disable-checking --disable-werror --enable-secureplt --disable-libunwind-exceptions --disable-multilib --enable-libmudflap --disable-libssp --enable-java-awt=gtk --enable-objc-gc --enable-languages=c,c++,java,objc,obj-c++,fortran --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 4.1.2 (Gentoo 4.1.2)

Where is the problem?

Thanks for explanations and have a nice day, Jiri Humpolicek



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Re: gcc warnings

[John Love-Jensen]

Hi Jiri,

It's valid C code to assign from a variable of greater type to one of
smaller type.

I think that this is very unfortunate.  I presume you do as well.  Alas.

You can act upon it programmatically, in runtime, if you do something like:

#include "stdio.h"

unsigned char LongAsUnsignedChar(long c)
{
  if(c > 255 || c < 0)
  {
    fprintf(stderr, "Error: %ld outside of 0,255 range\n", c);
  }

  return c;
}

int main()
{
  long a = 10000;
  unsigned char b = LongAsUnsignedChar(a);

  printf("%d\n", b);

  return b;
}

Alternatively, you can use a B&D language like Ada where such assignments
cannot happen silently and need explicit conversion.

HTH,
--Eljay

Re: gcc warnings

[Tom St Denis]

Humpolicek, Jiri - Acision wrote:
> Hi,
>             I have, from my point of view, strange problem. I want to tell gcc to report all compilation warnings, especially warnings about assigment from variable of greater type to variable with smaller type. For example, when I write following code and compile it with next command no warning is reported:
>
> c++ -o test test.cpp -Wall -Wextra -Wconversion -pedantic
>
> #include "stdio.h"
>
> int main()
> {
>         long a = 10000;
>         unsigned char b = a;
>
>         printf("%d\n", b);
>
>         return b;
> }
>
>   

The problem is that's not an error or problem as far as the C standard 
[and C++] goes.  So a warning for that while valid, would probably be 
out of line.

My recommendation is to simply not assign across types unless you have 
to.  If you have a function like

void myfunc(unsigned long somevalue)
{
}

Then never store somevalue in anything but an unsigned long unless 
you're sure of what you are doing.  Why would you write

char careless = somevalue;

just for the hell of it? 

Tom

RE: gcc warnings

[Humpolicek, Jiri - Acision]

>My recommendation is to simply not assign across types unless you have 
>to.  If you have a function like
>
>void myfunc(unsigned long somevalue)
>{
>}
>
>Then never store somevalue in anything but an unsigned long unless 
>you're sure of what you are doing.  Why would you write
>
>char careless = somevalue;
>
>just for the hell of it? 
>
>Tom

I fully understand with you Tom. I don't want to write this 'correct'
code, but problem is that it is easy to make this constructs
inadvertently. And IMHO this is place for compiler to report warning
'Here you overlook something'.

Because there is no reason do these things I think that warning is good
solution. And if someone want to use these language properties without
warning, it may be possible to use explicit cast to smaller type to
suppress warning (that is correct because there is evidence that user
knows about his doing).

Thanks, Jiri Humpolicek


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Re: gcc warnings

[Tim Prince]

Humpolicek, Jiri - Acision wrote:

>             I have, from my point of view, strange problem. I want to tell gcc to report all compilation warnings, especially warnings about assigment from variable of greater type to variable with smaller type. For example, when I write following code and compile it with next command no warning is reported:
> 
> c++ -o test test.cpp -Wall -Wextra -Wconversion -pedantic
> 
You don't say anything about what problem you encounter, or what
platform you use.  Your source code doesn't look like a suitable
replacement for a test command which may be implemented in your shell,
so it would be simpler to choose a non-conflicting name.

RE: gcc warnings

[Humpolicek, Jiri - Acision]

>>             I have, from my point of view, strange problem. I want to
>tell gcc to report all compilation warnings, especially warnings about
>assigment from variable of greater type to variable with smaller type.
For >example, when I write following code and compile it with next
command no >warning is reported:
>> 
>> c++ -o test test.cpp -Wall -Wextra -Wconversion -pedantic
>> 
>You don't say anything about what problem you encounter, or what
>platform you use.  Your source code doesn't look like a suitable
>replacement for a test command which may be implemented in your shell,
>so it would be simpler to choose a non-conflicting name.

I don't understand you. My problem is, that I am not able to force gcc
to report warnings when I assign bigger type to smaller type. So I
decided to ask someone to help me or give me any explanations of this
behaviour.

Jiri Humpolicek


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RE: gcc warnings

[Andrew Haley]

Humpolicek, Jiri - Acision writes:

 > This e-mail and any attachment is for authorised use by the
 > intended recipient(s) only. This email contains confidential
 > information. It should not be copied, disclosed to, retained or
 > used by, any party other than the intended recipient. Any
 > unauthorised distribution, dissemination or copying of this E-mail
 > or its attachments, and/or any use of any information contained in
 > them, is strictly prohibited and may be illegal. If you are not an
 > intended recipient then please promptly delete this e-mail and any
 > attachment and all copies and inform the sender directly via
 > email. Any emails that you send to us may be monitored by systems
 > or persons other than the named communicant for the purposes of
 > ascertaining whether the communication complies with the law and
 > company policies.

Quoting Ian Taylor,

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Andrew.

gcc warnings

[Zia Babar]

Title: gcc warnings





Hi,


I need some resource on the warnings and errors that gcc generates and I wonder if there is some literature available listing all the warnings and their probable causes. Actually I've been asked to debug some C project files and since I'm a newbie to C therefore most of the warnings generated by gcc during compilation escape me.

Thanks in advance.


Zia 

Re: gcc warnings

[Martin v. Loewis]

> I need some resource on the warnings and errors that gcc generates and I
> wonder if there is some literature available listing all the warnings and
> their probable causes. Actually I've been asked to debug some C project
> files and since I'm a newbie to C therefore most of the warnings generated
> by gcc during compilation escape me.

Please have a look at the section "Warning Options" in the gcc manual.

Regards,
Martin