CODEWITHSUNDEEP
cinitializationvalgrind
user3679622
user3679622

Reputation: 23

uninitialised value of size 8

I am Running a code for valgrind

int fun(char* str) {
    char* prt1;
    char* ptr2;
    char sstr[20];

    strcpy(sstr, "\0");

    ptr1 = str;
    ptr2 = sstr;

    while (((isspace(*ptr1)) || (iscntrl(*ptr1))) && (*ptr1 != '\0'))
        ptr1++;

    while (*ptr1 != '\0')
        *ptr2++ = *ptr1++;

    while (((isspace(*(ptr2 - 1))) || (iscntrl(*(ptr2 - 1)))) && (ptr2 > str))
        ptr2++;

    *ptr2 = '\0' strcpy(str, (S8*)sstr);

    return (strlen(ptr1));
}

getting this error Use of uninitialised value of size 8 for line 

while (((isspace (*(ptr2-1))) || (iscntrl (*(ptr2-1)))) &&
     (ptr2 > str))

If i put the NULLP check before assigning to the pointers this is error is gone

if (ptr1 != NULLP && ptr2 != NULLP) {
    ptr1 = str;
    ptr2 = sstr;
}

Is it with Valgrind code error or the check should be included ?

Thanks for the help .

Upvotes: 1

Views: 2092

Answers (2)

Ingo Leonhardt
Ingo Leonhardt

Reputation: 9904

No the check for NULLP is completely wrong and in fact invokes undefined behaviour as the pointers are not initialized at that time.

The real problem is that when you first enter the loop 

while (((isspace (*(ptr2-1))) || (iscntrl (*(ptr2-1)))) && (ptr2 > str))

you check the last char copied, and if that's a white space or control character you increment ptr2 and now you check the first char you have never initialized. (left aside the fact that the condition also is wrong for the case that you haven't copied any character. Then isspace(*(ptr2-1)) would invoke UB as well)

If you want to trim sstr (is it so?), your loop should be 

while ( ptr2 > sstr && ( isspace (ptr2[-1]) || iscntrl (ptr2[-1]) ) )
    ptr2--;

Note the differences:

  • compare ptr2 with sstr instead of str and do it first, so that isspace() and iscntrl() are not executed if ptr2 == sstr
  • ptr2-- instead of ptr2++

Upvotes: 3

ajclinto
ajclinto

Reputation: 145

I think if you change this line:

while (((isspace (*(ptr2-1))) || (iscntrl (*(ptr2-1)))) && (ptr2 > str))

to this:

while ((ptr2 > str) && ((isspace (*(ptr2-1))) || (iscntrl (*(ptr2-1)))))

You won't get the error. It looks like you could be reading before the beginning of str, since your check ptr2 > str will occur after the dereference. Moving this check to the beginning of the conditional allows it to short circuit.

Upvotes: 1

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