[sane-devel] [patch] fix SANE_Device

[Frank Zago]

Oliver Rauch wrote:
> Am Mit, 2004-11-17 um 20.58 schrieb fzago@austin.rr.com:
> 
>>>Hello Frank.
>>>
>>>I am not a fan of this patch.
>>>I think it will work but I think it is a hack.
>>>
>>>It seems that only a few backends have problems with this.
>>
>>A few backend are creating the name of the manufacturer from the scsi inquiry.
>>A lot of backends are creating their mode list from the device.
>>This patch will allow us to get rid of about 150 (IMO legitimate) warnings. The current code is not clean.
>>
>>
>>
>>>Why not fix it in a proper way:
>>
>>The non hack solution is to have two headers: one for the symbols exported and one for internal use. Same as what is done with the linux kernel structure s.
>>
>>
>>>create the strings as non const and then set the
>>>sane_device structur to point to these strings?!
>>
>>This will not work. That why there is so much warnings.
> 
> 
> IMO thats not ture.
> It is allowed to do this:
> 
> 	char *hello;
> 	const char *hello_const;
> 
>  	  hello="ABC";
> 
> 	  hello_const = hello;
> 
> 
> 
> and this produces a warning:
> 
> 	  *hello_const = 'A';
> 
> what is correct becaus we use a pointer to a const char to change the
> char so it is not const any more.
> 
> It is not a const pointer to a char, it is a pointer to a const char.
> And it is allowed to make a pointer of type pointer to const char point
> to a (non const) char.
> 
> I attach a little test c-code for this. Compile with
> 
> gcc consttest.c -o consttest -Wall
> 
> (gcc version 3.2.2 20030222)
> 
> Oliver
> 
> 
>>>But when I am the only one who is against this patch
>>>then I will be quiet and it will be ok for me. It is nothing
>>>that will steal my sleep :)
>>>
>>
>>Your input is appreciated. Thanks.
>>
>>Frank.
>>
>>
>>
>>
>>
>>
>>------------------------------------------------------------------------
>>
>>#include "stdio.h"
>>#include "stdlib.h"
>>
>>int main()
>>{
>> const char *hello_const;
>> char *hello;
>>
>>  printf("defining hello=\"Hello\"\n");
>>  printf("defining hello_const = hello\n");
>>  hello = "Hello";
>>  hello_const = hello;
>>  printf("hello = %s\n", hello);
>>  printf("hello_const = %s\n", hello_const);
>>  printf("\n");
>>
>>  printf("defining hello = (char *) malloc(10)\n");
>>  printf("defining *hello = \'A\'\n");
>>  printf("defining *(hello+1) = \'B\'\n");
>>  printf("defining hello_const = hello\n");
>>  hello= (char *) malloc(10);
>>  hello_const = hello;
>>  *hello='A';
>>  *(hello+1)='B';
>>  hello[2]=0;
>>  printf("hello = %s\n", hello);
>>  printf("hello_const = %s\n", hello_const);
>>  printf("\n");
>>
>>  printf("unallowed defining *hello_const = \'X\'\n");
>>  *hello_const='X';
>>
>>  printf("hello = %s\n", hello);
>>  printf("hello_const = %s\n", hello_const);
>>
>> return 0;
>>}

Your example is missing the one thing I'd like to see fixed. How do you free 
your memory allocated?
free(hello_const) will generate a warning.
free((void *)hello_const) will also generate a warning.

So do we fix:

dev->sane.name = strdup (devname);
...
free(dev->sane.name);


with:

unconst_name = strdup (devname);
dev->sane.name = unconst_name;
..
dev->sane.name = NULL;
free(unconst_name);


Or we fix dev->sane.name's definition

Or we do nothing and live with 150 warnings (for both SANE_Device and 
SANE_Descriptor)?

Frank.