Visual studio Run-Time Check Failure #2 - Stack around the variable 'temp' was corrupted

Question

I've written a function to partition elements for a quick sort algorithm for sorting an array of cstrings

void partition(char words[][MAXWORDLEN + 1], int start, int end, int& partitionIndex) {
char pivot[MAXWORDLEN + 1]; //choose last element to be the pivot
strcpy(pivot, words[end]);
partitionIndex = start; //partition index is initalized to the first index
for (int i = start; i < end; ++i) { //iterate through the array
    if (strcmp(words[i], words[end]) < 0) {
        char temp[MAXWORDLEN];
        strcpy(temp, words[i]); //swap the element with the element corresponding to the partition index
        strcpy(words[i], words[partitionIndex]);
        strcpy(words[partitionIndex], temp);
        partitionIndex++;
    }
}
cout << end << endl;
char temp[MAXWORDLEN + 1];
strcpy(temp, words[end]);
strcpy(words[end], words[partitionIndex]);
strcpy(words[partitionIndex], temp);

}

However, when I run the program, I get a run time check failure. MAXWORDLENGTH is 6 and all words in the array are between 4-6 characters long. So I'm confused why the variable temp can't seemed to be copied to words at index partitionIndex

Inside the `if` statement make it same also...That's what I meant. `temp[MAXWORDLEN+1]` — user2736738, Nov 18 '17 at 04:45
@coderredoc Oh lolll oops. But could you walk me through why the error seemed to occur on the last line on the function? — Howard Wang, Nov 18 '17 at 04:47
After the change that is mentioned there won't be that error. FYI that error is shown when you try to write too much data to a particular memory address. Here you are writing more to the string buffer that it can hold. — user2736738, Nov 18 '17 at 04:56

score 1 · Accepted Answer · answered Nov 18 '17 at 04:53

1

Change this:

char temp[MAXWORDLEN];

to this:

char temp[MAXWORDLEN + 1];

since the pivot array has this size too.

So when temp was of size 6 and the word it contains had 6 characters, the null terminator would be overwritten, meaning that the copy would fail and invoke Undefined Behavior. We don't really know what garbage values are going to be written into the target array via copying, if any.

answered Nov 18 '17 at 04:53

gsamaras

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Good @coderredoc,, but I think that this is the answer to the question. – gsamaras Nov 18 '17 at 04:58

Visual studio Run-Time Check Failure #2 - Stack around the variable 'temp' was corrupted

1 Answers1