Assign value is garbage or undefined

Question

I have posted screenshot of my error code. enter image description here

heights output

enter image description here

please any one can help me?

I suspect your for loop to assign the value in array han't executed...May be _numberOfColumns = 0. Can you print the contents of heights array? — Yogi, Mar 14 '13 at 10:10
Also, check if `malloc` has successfully allocated memory by checking `if(NULL == heights) printf("Not enough memory\n");` — melvynkim, Mar 14 '13 at 10:16
hi i checked code as your guys said, _numberOfColumns = 2 & height is not null. — Romit M., Mar 14 '13 at 10:21
@ravijimagna: continue wont affect any thing, That is waste however. — Anoop Vaidya, Mar 14 '13 at 10:22
@RomitMewada: One stupid suggestion, why dont you use NSMutableArray? — Anoop Vaidya, Mar 14 '13 at 10:23
It looks to me like the static analyzer is wrong; your code looks OK to me. — trojanfoe, Mar 14 '13 at 10:25
This looks OK. You should ignore the analyzer if code is working properly without any strange behaviour. — Yogi, Mar 14 '13 at 10:29
@trojanfoe The analyzer is correct, because `_numberOfColumns` could be 0, therefor making `heights[0]` garbage. — Sebastian, Mar 14 '13 at 10:39
@Sebastian No, the analyzer states that value **is** garbage, not **could be** garbage, so it's at least inaccurate. — trojanfoe, Mar 14 '13 at 10:40
@trojanfoe I've never seen the analyzer telling me that something **could be** wrong... — Sebastian, Mar 14 '13 at 10:44
@Sebastian So you've never seen the message "Potential leak of an object allocated on line ..."? — trojanfoe, Mar 14 '13 at 10:55

score 3 · Answer 1 · answered Mar 14 '13 at 10:47

I think the static analyzer is not seeing how _numberOfColumns can become non-zero, and hence its insistence that garbage is being assigned. You need to check that you are actually providing some means for _numberOfColumns to become non-zero.

Generally when I am writing loops that want to find the largest or the smallest value, I initialize the size variable to the largest (if I want the smallest) or smallest (if I want the largest) amount, and I think this will solve most of your issues:

float shortestHeight = FLT_MAX;
for (unsigned i = 0; i < _numberOfColumns; i++)
{
    // etc.
}

Sebastian · Answer 2 · 2013-03-15T11:31:41.347

The analyzer is correct. Your code will access garbage memory if _numberOfColumns is 0, thus allocating 0 bytes for heights, making heights[0] garbage. The analyzer doesn't know what values _numberOfColumns can have, but you can tell it by using assert(_numberOfColumns>0).

Take this C program for example:

int main(int argc, const char * argv[])
{
    int n = argc-1;
    int *a = malloc(n*sizeof(int));
    for (int i=0; i<n; i++) {
        a[i] = i;
    }
    int foo = a[0];
    free(a);
    return foo;
}

the size of a is determined by the number of arguments. If you have no arguments n == 0. If you are sure that your program (or just that part of your program) will always assign something greater than 0 to a, you can use an assertion. Adding assert(n>0) will tell the analyzer exactly that.

Assign value is garbage or undefined

2 Answers2