sizeof and access out of bound

[michele]

Hello,
During our internal review procedure we noticed a problem that cppcheck didn't point out. In the example attached it is used the "sizeof" of a variable instead of using the "countof", the number of elements. Cppcheck doensn't give any error in the for loop even if it's clear that we are going to have an access out of bound like the "sizeof" is not "managed".
In the last function I tested an explicit access out of bound and it correctly fired an error.
Regards
Michele

typedef enum
{
_e1 = (unsigned int)0,
_e2,
_e3,
_e4,
_e5,
_e6,
_e7,
_e8,
_e9,
_eTotalNumber
}tMyEnum;

void test1(void);
void test2(void);

void test1(void)
{
unsigned char zId;
unsigned char zTest;
static const tMyEnum cStg[] = {_e1, _e2, _e3};

for ( zId = 0; zId < sizeof( cStg ); zId++ )
{
if (cStg[zId] == _e8)
{
zTest = cStg[zId];
break;
}
}
}

void test2(void)
{
unsigned char zId;
unsigned char zTest;
static const tMyEnum cStg[] = {_e1, _e2, _e3};

for ( zId = 0; zId < sizeof( cStg ); zId++ )
{
if (cStg[zId] == _e8)
{
zTest = cStg[zId];
break;
}
}

zId = cStg[3]; //error is fired
}

Michele Ing. Corradin
Group Technologic Development
Sicon Srl
[cid:3256544718_62773626]

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[versat]

When the line

static const tMyEnum cStg[] = {_e1, _e2, _e3};

is changed to

static const int cStg[] = {_e1, _e2, _e3};

the issue is detected.
Looking at the debug output Cppcheck uses signed int for the enum values, so this issue could/should be detected i guess (at least as an inconclusive one).
I am not sure, but maybe Cppcheck intentionally does not warn about this because it can not be absolutely sure what type or better what size an enum has.
For some compilers (i think of embedded ones) one can enable to use the smallest type possible, so a char would be enough in this case. Then there would be no error.

I created this ticket for the issue:
https://trac.cppcheck.net/ticket/8438

[michele]

thank you for the support