This is another part of the backend code where valgrind is saying:
==5501== 5 errors in context 1 of 3:
==5501== Use of uninitialised value of size 8
==5501== at 0x5172AFC: ____strtod_l_internal (strtod_l.c:889)
==5501== by 0x403856: getRadiatingWifiList (automated_scanner.c:265)
==5501== by 0x403BDC: autoWirelessScanPlus (automated_scanner.c:386)
==5501== by 0x40400D: autoWirelessScanPlus_RN (automated_scanner.c:549)
==5501== by 0x402E2C: main (backend.c:251)
==5501== Uninitialised value was created by a stack allocation
==5501== at 0x4034BB: getRadiatingWifiList (automated_scanner.c:155)
The code portion is this:
tmp_wifi_quality =
calloc(sizeof(wifi_quality), 1);
Here follows testing of return value from calloc, but I am not quoting it.
active_wifi_list[*active_wifis] =
tmp_wifi_quality;
char* substr = strstr((char *) scan_buffer,
"Signal level=");
substr = strstr(substr, "=");
char* endstr = strstr(substr + 1, " ");
char tmpstr[MAX_ESSID_LENGTH];
strncpy(tmpstr, substr + 1, endstr - substr -
1);
tmpstr[endstr - substr + 1] = '\0';
tmp_wifi_quality->quality = strtod(tmpstr,
NULL);
Needless to state, the above works, but valgrind complains.
Edward
On 14/10/2015, Rainer Weikusat <rainerweiku...@virginmedia.com> wrote:
> Edward Bartolo <edb...@gmail.com> writes:
>> The problem according to my logic seems to be result is used in a
>> branch control expression before it is initialised. However, I am
>> emailing this to have other opinions.
>>
>>
>> int essid_alloc(
>> size_t length,
>> char ** result
>> ) {
>> char * tmp;
>>
>> if(length==0 || !result)
>> return EINVAL;
>>
>> tmp = (char *) calloc(length, 1);
>>
>> if(!tmp)
>> return ENOMEM;
>>
>> *result = tmp;
>>
>> return 0;
>> }
>
> result can't be uinitialized because it's an argument the caller must
> provide. *result may be uninitialized but this doesn't really matter
> unless the caller uses it regardless of the function return value. It
> would be helpful to know what valgrind actually prints.
>
> OTOH, the function above is equivalent to just doing a
>
> char *essid;
>
> essid = calloc(length, 1);
> if (!essid) /* ENOMEM */
>
> in the caller and IMHO, the whole function should be removed. There's
> also no point in casting the result of any memory allocation routine _in
> C_ as a void * will automatically be converted to whatever type was
> asked for on assignment (and there are rare cases where this may mask an
> actual error[*]).
>
> [*] In particular, using calloc without a prototype in scope will cause
> the compiler to assume that it returns and int. This will work on a
> 32-bit system because the sizeof of a pointer is == sizeof(int) but
> will fail on 64-bit (I had to mispleasure to debug this once when
> moving some 'working' 32-bit Linux code to Solaris 8 on Sparc ...).
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